Pressure-Sensitive Touch Panel

ABSTRACT

An apparatus for combined capacitance and pressure sensing is described. The apparatus includes a multiplexer ( 75 ) having a plurality of inputs ( 76 ) and an output (F), a touch panel ( 29 ), and a front end module ( 3 ). The touch panel includes a layer structure ( 5 ; FIG.  15 ) comprising one or more layers, each extending perpendicularly to a thickness direction, the one or more layers including a layer of piezoelectric material ( 10 ; FIG.  15 ), the layer structure having first ( 6 ) and second ( 7 ; FIG.  15 ) opposite faces, and the layer(s) arranged between the first and second faces such that the thickness direction of each layer is perpendicular to the first and second faces. The touch panel also includes a plurality of first electrodes ( 8 ) disposed on the first face, each first electrode connected to a respective input of the multiplexer. The touch panel also includes at least one second electrode ( 9 ) disposed on the second face. The front end module is configured to receive an input signal ( 11 ) from the multiplexer output. The front end module includes a first stage ( 12 ) configured to provide an amplified signal based on the input signal, and a second stage comprising first ( 13 ) and second ( 14 ) frequency-dependent filters configured to receive the amplified signal and to provide respective first ( 16 ) and second ( 17 ) filtered signals. The first filtered signal has a first frequency bandwidth, and the second filtered signal has a second frequency bandwidth which has a relatively higher start-frequency than the first frequency bandwidth.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/539,038, filed Jun. 22, 2017, which application is a 35 U.S.C. § 371application of PCT/GB2015/054157, which was filed on Dec. 23, 2015, andclaims the benefit under 35 U.S.C. § 119(e) to U.S. provisionalapplication No. 62/095,853, filed Dec. 23, 2014, and further claims thebenefit of priority from United Kingdom Application 1512621.2, filedJul. 17, 2015, and PCT Application No. PCT/GB2015/054087, filed Dec. 18,2015, all of which are incorporated by reference as if fully disclosedherein.

FIELD OF THE INVENTION

The present invention relates to a touch panel for combined capacitiveand pressure sensing.

BACKGROUND

Resistive and capacitive touch panels are used as input devices forcomputers and mobile devices. One type of capacitive touch panel,projected capacitance touch panels, is often used for mobile devicesbecause an exterior layer may be made of glass, providing a hard surfacewhich is resistant to scratching. An example of a projected capacitancetouch panel is described in US 2010/0079384 A1.

Projected capacitance touch panels operate by detecting changes inelectric fields caused by the proximity of a conductive object. Thelocation at which a projected capacitance touch panel is touched isoften determined using an array or grid of capacitive sensors. Althoughprojected capacitance touch panels can usually differentiate betweensingle-touch events and multi-touch events, they suffer the drawback ofnot being able to sense pressure. Thus, projected capacitance touchpanels tend to be unable to distinguish between a relatively light tapand a relatively heavy press. A touch panel which can sense pressure canallow a user to interact with a device in new ways by providingadditional information to simply position of a touch.

Different approaches have been proposed to allow a touch panel to sensepressure. One approach is to provide capacitive sensors which include agap whose size can be reduced by applied pressure, so as to produce ameasureable difference in the mutual capacitance. For example, US2014/043289 A describes a pressure sensitive capacitive sensor for adigitizer system which includes an interaction surface, at least onesensing layer operable to sense interaction by mutual capacitivesensing, and an additional layer comprising resilient properties andoperable to be locally compressed responsive to pressure locally appliedduring user interaction with the capacitive sensor. However, the needfor a measureable displacement can make it more difficult to use a glasstouch surface and can cause problems with material fatigue afterrepeated straining.

Other pressure sensitive touch panels have proposed using one or morediscrete force sensors supporting a capacitive touch panel, such thatpressure applied to the capacitive touch panel is transferred to one ormore sensors located behind the panel or disposed around the periphery.For example, US 2003/0076646 A1 describes using strain gauges with aforce sensor interface which can couple to touch circuitry. WO2012/031564 A1 describes a touch panel including a first panel, a secondpanel, and a displacement sensor sandwiched between the first panel andthe second panel. The displacement sensors, such as capacitive orpiezoresistive sensors, are placed around the edge of the second panel.However, it can be difficult to distinguish the pressure of multipletouches using sensors located behind a touch panel or disposed aroundthe periphery.

Other pressure sensitive touch panels have been proposed which attemptto combine capacitive touch sensing with force sensitive piezoelectriclayers. For example, WO 200009/150498 A2 describes a device including afirst layer, a second layer, a third layer, a capacitive sensingcomponent coupled to the first layer, and a force sensing componentcoupled to the first layer and the third layer and configured to detectthe amount of force applied to the second layer. WO 2015/046289 A1describes a touch panel formed by stacking a piezoelectric sensor and anelectrostatic sensor. The piezoelectric sensor is connected to apressing force detection signal generation unit, and the electrostaticsensor is connected to a contact detection signal generation unit.However, systems which use separate electronics to sense changes incapacitance and pressures can make a touch panel more bulky andexpensive. Systems in which electrodes are directly applied or patternedonto a piezoelectric film can be more complex and expensive to produce.

SUMMARY

The present invention seeks to provide an improved capacitive touchpanel.

According to a first aspect of the invention there is provided apparatusincluding a multiplexer having a plurality of inputs and an output. Theapparatus also includes a touch panel including a layer structureincluding one or more layers, each layer extending perpendicularly to athickness direction. The one or more layers include a layer ofpiezoelectric material. The layer structure has first and secondopposite faces. The one or more layer(s) are arranged between the firstand second faces such that the thickness direction of each layer isperpendicular to the first and second faces. The layer structureincludes a plurality of first electrodes disposed on the first face,each first electrode connected to a respective input of the multiplexer.The layer structure includes at least one second electrode disposed onthe second face. The apparatus includes a front end module configured toreceive an input signal from the multiplexer output. The front endmodule includes a first stage configured to provide an amplified signalbased on the input signal. The front end module includes a second stageincluding first and second frequency-dependent filters configured toreceive the amplified signal and to provide respective first and secondfiltered signals. The first filtered signal has a first frequencybandwidth, and the second filtered signal has a second frequencybandwidth which has a relatively higher start-frequency than the firstfrequency bandwidth.

Thus, pressure and capacitance measurements may be performed using atouch panel without the need for separate pressure and capacitanceelectrodes. A single input signal is received from an electrodeincluding pressure and capacitance information and the input signal maybe amplified and processed using a single front end. This can allow theapparatus to be more readily integrated into existing projectedcapacitance touch panels and/or to be easily used in conjunction withexisting devices such as touch controller ICs.

The apparatus may further include a signal source configured to providea periodic signal. The front end module may be configured to receive theperiodic signal and the first stage may be configured to provide theamplified signal based on the input signal and the periodic signal. Thesecond filtered signal may be based on the periodic signal and the firstfiltered signal may be not based on the periodic signal.

Providing a periodic signal to the front end module instead of throughthe touch panel electrodes directly can allow the gain for amplifyingsignals from the layer of piezoelectric material to be increased withoutcausing saturation of the first stage output. It can allow ananalogue-to-digital converter (ADC) to be used in a subsequent stagehaving a lower dynamic range.

The signal source may provide a periodic signal having a basic frequencyof at least 0.5 kHz, optionally at least 1 kHz, optionally at least tokHz. The signal source may provide a periodic signal having a basicfrequency of at least 20 kHz. The signal source may provide a periodicsignal having a basic frequency of at least 50 kHz. The signal sourcemay provide a periodic signal having a basic frequency of at least 100kHz. The signal source may provide a periodic signal having asinusoidal, square, triangular or saw-toothed waveform. The signalsource may provide a periodic signal comprising a superposition of twoor more sinusoidal waveforms having different frequencies. The signalsource may be a digital-to-analogue converter (DAC).

The apparatus may include a controller configured to cause themultiplexer to connect each one of the plurality of first electrodes tothe front end module according to a sequence determined by thecontroller. The sequence may be pre-determined. The sequence may bedynamically determined.

The first and second stages may be configured such that the amplitude ofthe first filtered signal is dependent upon a pressure applied to thelayer of piezoelectric material proximate to a given first electrodeconnected to the front end module by the multiplexer.

The first and second stages may be configured such that the amplitude ofthe second filtered signal is dependent upon a capacitance of a givenfirst electrode connected to the front end module by the multiplexer.The amplitude of the second filtered signal may depend upon aself-capacitance associated with a given first electrode. The amplitudeof the second filtered signal may depend upon a mutual capacitancebetween the given first electrode and the second electrode(s).

The first frequency-dependent filter may comprise a low-pass filter andthe second frequency-dependent filter may comprise at least oneband-pass filter. The first frequency-dependent filter may comprise atleast one band-stop filter and the second frequency-dependent filter maycomprise at least one band-pass filter. The first frequency-dependentfilter may comprise a low-pass filter and the second frequency-dependentfilter may comprise a high-pass filter. Each band-pass filter may be anotch filter. Each band-stop filter may be a notch filter. Filters maycomprise active filter circuits. Filters may comprise passive filtercircuits. Filters may comprise a single stage. Filters may comprisemultiple stages. Filters may comprise filter circuits selected from thegroup consisting of Butterworth filters, Chebyshev filters, Gaussianfilters and Bessel filters.

The first stage may have a low-frequency cut-off configured to reject apyroelectric response of the layer of piezoelectric material. The firststage may have a low-frequency cut-off configured to reject a mainspower distribution frequency. The low frequency cut-off may be at least50 Hz. The low frequency cut-off may be 60 Hz. The low frequency cut-offmay be at least 100 Hz. The low frequency cut-off may be at least 200Hz.

The first stage may include one or more integrating amplifiersconfigured to integrate the input signal.

The first stage may include one or more differential amplifier(s)configured to receive the input signal.

The plurality of first electrodes may include a plurality of conductivepads disposed on the first face in a two dimensional array.

The touch panel may further include a plurality of third electrodesdisposed overlying the first face of the layer structure and arrangedsuch that the layer structure is between the plurality of thirdelectrodes and the second electrode(s). Each of the plurality of thirdelectrodes may be connected to a respective input of the multiplexer.

The apparatus may include a controller configured to cause themultiplexer to connect each one of the plurality of first electrodes andeach one of the plurality of third electrodes to the front end moduleaccording to a sequence determined by the controller.

The apparatus may further include a second multiplexer having aplurality of inputs and an output. The apparatus may further include asecond front end module configured to receive an input signal from theoutput of the second multiplexer. The second front end module may havethe same electronic configuration as the front end module. The touchpanel may further include a plurality of third electrodes disposedoverlying the first face of the layer structure and arranged such thatthe layer structure lies between the plurality of third electrodes andthe second electrode(s). Each third electrode may be connected to arespective input of the second multiplexer.

The apparatus may include a controller configured to cause the secondmultiplexor to connect each one of the plurality of third electrodes tothe second front end module according to a sequence determined by thecontroller.

Each first electrode may extend in a first direction and the pluralityof first electrodes may be arrayed spaced apart perpendicular to thefirst direction. Each third electrode may extend in a second directionand the plurality of third electrodes may be arrayed spaced apartperpendicular to the second direction. The first and second directionsmay be different. The first and second directions may be substantiallyperpendicular. The first and second directions may meet at an angle ofmore than 30 and less than 90 degrees.

The touch panel may further include a second layer structure includingone or more dielectric layers. Each dielectric layer may extendperpendicularly to a thickness direction. The second layer structure mayhave third and fourth opposite faces. The dielectric layers may bearranged between the third and fourth faces such that the thicknessdirection of each dielectric layer is perpendicular to the third andfourth faces. The plurality of third electrodes may be disposed on thethird face of the second layer structure and the fourth face of thesecond layer structure may contact the first plurality of electrodes.

The plurality of third electrodes may be disposed on the first face ofthe layer structure. Each first electrode may comprise a continuousconductive region and each third electrode may comprise a plurality ofconductive regions electrically connected to one another by jumpers.Each jumper may span a conductive region forming a portion of one of thefirst electrodes.

The apparatus may further include a second multiplexer having aplurality of inputs and an output. The apparatus may further include asecond front end module configured to receive an input signal from theoutput of the second multiplexer. The second front end module may havethe same electronic configuration as the front end module. The touchpanel may include a plurality of second electrodes. The touch panel mayfurther include a plurality of third electrodes disposed on the secondface of the layer structure. Each third electrode may be connected to arespective input of the second multiplexer. Each first electrode mayextend in a first direction and the plurality of first electrodes may bearrayed spaced apart perpendicular to the first direction. Each secondelectrode may extend in a second direction and the plurality of secondelectrodes may be arrayed spaced apart perpendicular to the seconddirection. Each third electrode may extend in a second direction and theplurality of third electrodes may be arrayed spaced apart perpendicularto the second direction. The third electrodes may be arranged parallelto and be interleaved with the plurality of second electrodes. The firstand second directions may be different. The first and second directionsmay be substantially perpendicular. The first and second directions maymeet at an angle of more than 30 and less than 90 degrees.

The layer structure may include one or more dielectric layers stackedbetween the layer of piezoelectric material and the first face of thelayer structure.

The layer structure may include one or more dielectric layers stackedbetween the second face of the layer structure and the layer ofpiezoelectric material.

Thus, none of the electrodes need to be disposed directly on the layerof piezoelectric material. This allows a bare layer of piezoelectricmaterial to be included in the layer structure. This can reduce thecosts and complexity of producing the layer structure.

The second electrode may be a region of conductive material which issubstantially coextensive with the second face.

The at least one second electrode may be a region of conductive materialarranged in a grid.

The signal source may include a voltage controlled source, and theapparatus may further include a bias source coupled to the secondelectrode(s). The bias source may provide a constant bias. The constantbias may be ground potential. The bias source may be provided by thesignal source.

The signal source may include one or more synchronized currentcontrolled sources, and each current controlled source may provide theperiodic signal to a respective front end module.

The first stage of each front end module may include an operationalamplifier having at least an inverting input coupled to a first rail, anon-inverting input coupled to the voltage controlled source via a pathcomprising a first resistor, and an output coupled to a second rail. Thefirst stage of each front end module may include a second resistorcoupling the first rail to the output of the multiplexer correspondingto the front end module, a third resistor coupling the first rail to thesecond rail, and a first capacitor coupling the first rail to the secondrail. The second rail may provide the amplified signal.

A second capacitor may be connected in parallel with the first resistor.The capacitance of the first capacitor may be substantially equal to amutual capacitance between a given first electrode and at least onesecond electrode.

The first stage of each front end module may include a first operationalamplifier having at least an inverting input coupled to a first rail, anon-inverting input coupled to the voltage source via a path comprisinga first resistor and a second rail, and an output coupled to a thirdrail. The first stage of each front end module may include a secondoperational amplifier having at least an inverting input coupled to afourth rail, a non-inverting input coupled to the second rail via a pathcomprising a second resistor, and an output coupled to a fifth rail. Thefirst stage of each front end module may include a comparator having atleast an inverting input coupled to the third rail, a non-invertinginput coupled to the fifth rail, and an output providing the amplifiedsignal. The first stage of each front end module may include a thirdresistor coupling the first rail output of the multiplexer correspondingto the front end module, a fourth resistor coupling the first rail tothe third rail, a first capacitor coupling the first rail to the thirdrail, a fifth resistor coupling the fourth rail to the fifth rail, asecond capacitor coupling the fourth rail to the fifth rail, and a sixthresistor coupling the fourth rail to ground via a path comprising athird capacitor.

The first resistor may have a resistance substantially equal to thesecond resistor. The third resistor may have a resistance substantiallyequal to the sixth resistor. The fourth resistor may have a resistancesubstantially equal to the fifth resistor. The first capacitor may havea capacitance substantially equal to the second capacitor. The thirdcapacitor may have a capacitance substantially equal to a mutualcapacitance between the given first electrode and at least one secondelectrode. A fourth capacitor may be connected in parallel with thefirst resistor. A fifth capacitor may be connected in parallel with thesecond resistor.

The first stage of each front end module may include an operationalamplifier having at least an inverting input coupled to a first currentcontrolled source via a first rail, a non-inverting input coupled toground via a path comprising a first resistor, and an output coupled toa second rail. The first stage of each front end module may include asecond resistor coupling the first rail to the second rail, and a thirdresistor coupling the first rail to ground via a path comprising a firstcapacitor. The first rail may be coupled to the output of themultiplexer corresponding to the front end module and the second railmay be coupled to the second electrode(s). The first rail may be coupledto the second electrode(s) and the second rail may be coupled to theoutput of the multiplexer corresponding to the front end module. Thesecond rail may provide the amplified signal.

A second capacitor may be connected in parallel with the first resistor.The first capacitor may have a capacitance substantially equal to amutual capacitance between the given first electrode and at least onesecond electrode.

The first stage of each front end module may include a first operationalamplifier having at least an inverting input coupled to a first currentcontrolled source via a first rail, a non-inverting input coupled toground via a path comprising a first resistor, and an output coupled toa second rail. The first stage of each front end module may include asecond operational amplifier having at least an inverting input coupledto a second current source by a third rail, a non-inverting inputcoupled to ground via a path comprising a second resistor, and an outputcoupled to a fourth rail. The first stage of each front end module mayinclude a comparator having at least an inverting input coupled to thesecond rail, a non-inverting input coupled to the fourth rail, and anoutput providing the amplified signal. The first stage of each front endmodule may include a third resistor coupling the first rail and thesecond rail, a fourth resistor coupling the first rail to ground via apath comprising a first capacitor, a fifth resistor coupling the thirdrail to ground via a path comprising a second capacitor, a sixthresistor coupling the third rail to the fourth rail, and a thirdcapacitor coupling the third rail to the fourth rail. The first rail maybe coupled to the output of the multiplexer corresponding to the frontend module and the second rail may be coupled to the secondelectrode(s). The first rail may be coupled to the second electrode(s)and the second rail may be coupled to the output of the multiplexercorresponding to the front end module. The first current controlledsource may be synchronised with the second current controlled source.

The third resistor may have a resistance substantially equal to thesixth resistor. The first capacitor may have a capacitance substantiallyequal to the second capacitor. The third capacitor may have acapacitance substantially equal to a mutual capacitance between thegiven first electrode and at least one second electrode. A fourthcapacitor may be connected in parallel with the first resistor. A fifthcapacitor may be connected in parallel with the second resistor.

The apparatus may further comprise a signal processor arranged toreceive the first and second filtered signals and to calculate pressurevalues and/or capacitance values in dependence upon the first and secondfiltered signals.

The signal processor may be configured to employ correlated doublesampling methods so as to improve signal to noise ratio of the pressurevalues and/or capacitance values. The signal processor may be configuredto treat the pressure values and/or the capacitance values as imagedata.

According to a second aspect of the invention there is provided a devicefor processing signals from a projected capacitance touch panel, thepanel including a layer of piezoelectric material disposed between aplurality of first electrodes and at least one second electrode. Thedevice configured, in response to receiving signals from a given firstelectrode, to generate a pressure signal indicative of a pressureapplied to the touch panel proximate to the given first electrode and acapacitance signal indicative of a capacitance of the given firstelectrode.

The device may include at least one signal splitter stage configured tosplit signals received from the touch panel into first and secondsignals, to pass the first signals to a first frequency dependent filterconfigured to reject the pressure signal and pass the capacitancesignal, and to pass the second signals to a second frequency dependentfilter configured to reject the capacitance signal and pass the pressuresignal.

The device may include at least one amplification stage configured toamplify the pressure signal. The amplification stage may be configuredto receive signals from the given first electrode and to provide anamplified signal to the signal splitter stage. The amplified signal mayinclude a superposition of the capacitance signal and the pressuresignal. The device is configured to separate the capacitance signal andthe pressure signal. The device may include a signal source configuredto generate a periodic signal. The amplification stage may be configuredto receive the periodic signal. The capacitance signal may be based onthe periodic signal. The pressure signal may not be based on theperiodic signal. The signals received from the given first electrode mayinclude a superposition of the capacitance signal and the pressuresignal.

Apparatus may include a projected capacitance touch panel, the panelincluding a layer of piezoelectric material disposed between a pluralityof first electrodes and at least one second electrode, and the device.The device may further include a plurality of terminals, each terminalconnected to a corresponding first electrode.

The device may be configured to receive signals from each firstelectrode concurrently. The device may include an amplification stageand a signal splitter stage corresponding to each terminal.

The device may be configured to receive signals from each firstelectrode sequentially. The device may include one amplification stageand one signal splitter stage and the plurality of terminals may beconnected to the amplification stage through a multiplexer. Themultiplexer may be configured to connect each of the terminals to theamplification stage according to a sequence.

Apparatus may include a projected capacitance touch panel, the panelincluding a layer of piezoelectric material disposed between a pluralityof first electrodes and at least one second electrode, a multiplexerhaving a plurality of inputs and an output, each multiplexer inputconnected to a corresponding first electrode, and the device. The devicemay further include a terminal connected to the multiplexer output.

The apparatus may further include a signal processor arranged to receivethe pressure and capacitance signals and to calculate pressure valuesand capacitance values in dependence upon the pressure and capacitancesignals.

The signal processor may be configured to employ correlated doublesampling methods so as to improve signal to noise ratio of the pressurevalues and/or capacitance values. The signal processor may be configuredto treat the pressure values and/or the capacitance values as imagedata.

According to a third aspect of the invention there is provided aportable electronic device comprising the apparatus.

According to a fourth aspect of the invention there is provided a methodin a touch panel including a layer structure comprising one or morelayers, each layer extending perpendicularly to a thickness direction,the one or more layers including a layer of piezoelectric material, thelayer structure having first and second opposite faces, and the layer(s)arranged between the first and second faces such that the thicknessdirection of each layer is perpendicular to the first and second faces,a plurality of first electrodes disposed on the first face, and at leastone second electrode disposed on the second face. The method includesselecting each given first electrode of the plurality of firstelectrodes according to a predetermined sequence. The method includes,for each given first electrode, generating an amplified signal based onan input signal received from the given first electrode, filtering theamplified signal using a first frequency-dependent filter to provide afirst filtered signal having a first frequency bandwidth, and filteringthe amplified signal using a second frequency-dependent filter toprovide a second filtered signal having a second frequency bandwidthwhich has a relatively higher start-frequency than the first frequencybandwidth.

The method may further include providing a periodic signal. Theamplified signal may be generated based on the input signal and theperiodic signal. The second filtered signal may be based on the periodicsignal and the first filtered signal may be based on the periodicsignal.

The method may include processing the first filtered signal to calculatepressure values. The method may include processing the second filteredsignal to calculate capacitance values. The method may include treatingthe pressure values and/or the capacitance values as image data. Themethod may include treating the pressure values as a pressure image inwhich each pixel value is a pressure value corresponding to a locationof the touch panel. The method may include treating the capacitancevalues as a capacitance image in which each pixel value is a capacitancevalue corresponding to a location of the touch panel. The method mayinclude applying correlated double sampling methods to the pressureimage and/or the capacitance image.

According to a fifth aspect of the invention there is provided a methodof processing signals from a projected capacitance touch panel, thepanel including a layer of piezoelectric material disposed between aplurality of first electrodes and at least one second electrode. Themethod includes receiving signal(s) from a given first electrode. Themethod also includes generating, based on the received signal(s), apressure signal indicative of a pressure applied to the touch panelproximate to the given first electrode. The method also includesgenerating, based on the received signal(s), a capacitance signalindicative of a capacitance of the given first electrode.

The method may include splitting the received signal(s) into first andsecond signal(s). Generating the capacitance signal may includingfiltering the first signal(s) using a first frequency dependent filterto reject the pressure signal and pass the capacitance signal.Generating the pressure signal may include filtering the secondsignal(s) using a second frequency dependent filter to reject thecapacitance signal and pass the pressure signal.

The method may include amplifying the pressure signal. The method mayinclude generating an amplified signal in dependence upon signalsreceived from the given first electrode. The amplified signal mayinclude a superposition of the capacitance signal and the pressuresignal. The method may include separating the capacitance signal and thepressure signal. The method may include receiving a periodic signal. Theamplified signal may be generated in dependence upon the signalsreceived from the given first electrode and the periodic signal. Thecapacitance signal may be based on the periodic signal. The pressuresignal may not be based on the periodic signal. The signals receivedfrom the given first electrode may include a superposition of thecapacitance signal and the pressure signal.

The method may include receiving signals from the plurality of firstelectrodes concurrently. The method may include receiving signals fromthe plurality of first electrodes sequentially.

The method may include processing the pressure signal to calculatepressure values. The method may include processing the capacitancesignal to calculate capacitance values. The method may include treatingthe pressure values and/or the capacitance values as image data. Themethod may include treating the pressure values as a pressure image inwhich each pixel value is a pressure value corresponding to a locationof the touch panel. The method may include treating the capacitancevalues as a capacitance image in which each pixel value is a capacitancevalue corresponding to a location of the touch panel. The method mayinclude applying correlated double sampling methods to the pressureimage and/or the capacitance image.

According to a sixth aspect of the invention there is provided aportable electronic device carrying out the method.

According to a seventh aspect of the invention there is provided acomputer program product stored on a non-transitory computer readablestorage medium which, when executed by a data processing apparatus,causes the data processing apparatus to execute the method.

According to an eighth aspect of the invention there is provided amethod of fabricating a layer structure for a touch panel. The methodincludes providing a transparent substrate having first and secondopposite faces. The method includes providing a dielectric layer havingfirst and second opposite faces. The method includes providing a layerof piezoelectric material having first and second opposite faces. Themethod includes providing a plurality of first conductive regionsextending in a first direction and spaced apart perpendicular to thefirst direction. The method includes providing a plurality of secondconductive regions extending in a second direction and spaced apartperpendicular to the second direction, the second direction different tothe first. The method includes providing a third conductive materialregion extending such that, when assembled, the third conductivematerial region at least partially overlaps each first conductive regionand each third conductive region. The method includes assembling thelayer structure such that the first face of the transparent substrate isopposed to the second face of the dielectric layer, and the first faceof the dielectric layer is opposed to the second face of the layer ofpiezoelectric material. The method includes assembling the layerstructure such that the plurality of first conductive regions aredisposed between the transparent substrate and the dielectric layer, theplurality of second conductive regions are disposed between thetransparent substrate and the layer of piezoelectric material, and thethird conductive material region is disposed over the first face of thelayer of piezoelectric material.

Thus, the layer structure for a touch panel can be fabricated withoutthe need for complex and/or expensive deposition of patterned electrodeon the layer of piezoelectric material. Additionally, the layer ofpiezoelectric material may be provided as a single sheet without theneed to deposit or pattern piezoelectric material regions to providediscrete devices.

The plurality of first conductive regions may be disposed on the secondface of the dielectric layer. Assembling the layer structure may includebonding the second face of the dielectric layer to the first face of thetransparent substrate.

The plurality of first conductive regions may be disposed on the firstface of the transparent substrate. Assembling the layer structure mayinclude bonding the second face of the dielectric layer to the firstface of the transparent substrate.

The plurality of first conductive regions may be disposed on the firstface of the dielectric layer. Assembling the layer structure may includebonding the second face of the dielectric layer to the first face of thetransparent substrate.

The plurality of second conductive regions may be disposed on the sameface of the dielectric layer as the plurality of first electrodes. Eachfirst conductive region may be a continuous conductive region and eachsecond conductive region may be a plurality of separate conductiveregions connected by jumpers. Each jumper may span a portion of a firstconductive region. Assembling the layer structure may include bondingthe second face of the layer of piezoelectric material to the first faceof the dielectric layer.

The plurality of second conductive regions may be disposed on the firstface of the dielectric layer. Assembling the layer structure may includebonding the second face of the layer of piezoelectric material to thefirst face of the dielectric layer.

The method may further include providing a second dielectric layerhaving first and second opposite faces. The plurality of secondconductive regions may be disposed on the first face or the second faceof the second dielectric layer. Assembling the layer structure mayinclude bonding the second face of the second dielectric layer to thefirst face of the dielectric layer, and bonding the second face of thelayer of piezoelectric material to the first face of the seconddielectric material layer.

The plurality of second conductive regions may be disposed on the secondface of the layer of piezoelectric material. The method may furtherinclude bonding the second face of the layer of piezoelectric materialto the first face of the dielectric layer.

The method may further include providing a third dielectric layer havingfirst and second opposite faces. The third conductive material regionmay be disposed on the first face or the second face of the thirddielectric layer. Assembling the layer structure may include bonding thesecond face of the third dielectric layer to the first face of the layerof piezoelectric material.

The third conductive material region may be disposed on the first faceof the layer of piezoelectric material.

Bonding a second face of one layer to a first face of another layer mayinclude providing a layer of pressure sensitive adhesive materialbetween the opposed first and second faces, and applying pressurebetween the first and second faces. “Pressure sensitive adhesive” (PSA)as used herein includes optically clear adhesives (OCA), optically clearresins (OCR) and liquid optically clear adhesives (LOCA).

According to a ninth aspect of the invention there is provided aportable electronic device comprising a layer structure for a touchpanel fabricated according to the method.

According to a tenth aspect of the invention there is provided a methodof fabricating a layer structure for a touch panel. The method includesproviding a transparent substrate having first and second oppositefaces, providing a first dielectric layer having first and secondopposite faces, wherein a plurality of first conductive regionsextending in a first direction and spaced apart perpendicular to thefirst direction are disposed on the second face of the first dielectriclayer, and bonding the second face of the first dielectric layer to thefirst face of the transparent substrate. The method includes providing asecond dielectric layer having first and second opposite faces, whereina plurality of second conductive regions extending in a second directionand spaced apart perpendicular to the second direction are disposed onthe second face of the second dielectric layer, and wherein the seconddirection is different to the first direction, and bonding the secondface of the second dielectric layer to the first face of the firstdielectric layer. The method includes providing a layer of piezoelectricmaterial having first and second opposite faces, wherein a thirdconductive material region is disposed on the first face of the layer ofpiezoelectric material such that, when assembled, the third conductiveregion at least partially overlaps each first conductive region and eachsecond conductive region, and bonding the second face of the layer ofpiezoelectric material to the first face of the second dielectric layer.

According to an eleventh aspect of the invention there is provided amethod of fabricating a layer structure for a touch panel. The methodincludes providing a transparent substrate having first and secondopposite faces, providing a dielectric layer having first and secondopposite faces, wherein a plurality of first conductive regionsextending in a first direction and spaced apart perpendicular to thefirst direction are disposed on the second face of the dielectric layer,and bonding the second face of the dielectric layer to the first face ofthe transparent substrate. The method includes providing a layer ofpiezoelectric material having first and second opposite faces, wherein aplurality of second conductive regions extending in a second directionare and spaced apart perpendicular to the second direction are disposedon the second face of the layer of piezoelectric material, wherein thesecond direction is different to the first direction, and wherein athird conductive material region is disposed on the first face of thelayer of piezoelectric material such that, when assembled, the thirdconductive region at least partially overlaps each first conductiveregion and each second conductive region, and bonding the second face ofthe layer of piezoelectric material to the first face of the dielectriclayer.

According to a twelfth aspect of the invention there is provided amethod of fabricating a layer structure for a touch panel. The methodincludes providing a transparent substrate having first and secondopposite faces, providing a first dielectric layer having first andsecond opposite faces, wherein a plurality of first conductive regionsextending in a first direction and spaced apart perpendicular to thefirst direction are disposed on the second face of the first dielectriclayer, and bonding the second face of the first dielectric layer to thefirst face of the transparent substrate. The method includes providing asecond dielectric layer having first and second opposite faces, whereina plurality of second conductive regions extending in a second directionand spaced apart perpendicular to the second direction are disposed onthe second face of the second dielectric layer, and wherein the seconddirection is different to the first direction, and bonding the secondface of the second dielectric layer to the first face of the firstdielectric layer. The method includes providing a layer of piezoelectricmaterial having first and second opposite faces, and bonding the secondface of the layer of piezoelectric material to the first face of thesecond dielectric layer. The method includes providing a thirddielectric layer having first and second faces, wherein a thirdconductive material region is disposed on the second surface of thethird dielectric layer such that, when assembled, the third conductiveregion at least partially overlaps each first conductive region and eachsecond conductive region, and bonding the second face of the thirddielectric layer to the first face of the layer of piezoelectricmaterial.

According to a thirteenth aspect of the invention there is provided amethod of fabricating a layer structure for a touch panel. The methodincludes providing a transparent substrate having first and secondopposite faces, providing a dielectric layer having first and secondopposite faces, wherein a plurality of first conductive regionsextending in a first direction and spaced apart perpendicular to thefirst direction are disposed on the second face of the dielectric layer,and wherein a plurality of second conductive regions extending in asecond direction and spaced apart perpendicular to the second directionare disposed on the first face of the dielectric layer, and wherein thesecond direction is different to the first direction, and bonding thesecond face of the dielectric layer to the first face of the transparentsubstrate. The method includes providing a layer of piezoelectricmaterial having first and second opposite faces, wherein a thirdconductive material region is disposed on the first face of the layer ofpiezoelectric material such that, when assembled, the third conductiveregion at least partially overlaps each first conductive region and eachsecond conductive region, and bonding the second face of the layer ofpiezoelectric material to the first face of the dielectric layer.

According to a fourteenth aspect of the invention there is provided amethod of fabricating a layer structure for a touch panel. The methodincluding providing a transparent substrate having first and secondopposite face, providing a first dielectric layer having first andsecond opposite faces, wherein a plurality of first conductive regionsextending in a first direction and spaced apart perpendicular to thefirst direction are disposed on the second face of the first dielectriclayer, and wherein a plurality of second conductive regions extending ina second direction and spaced apart perpendicular to the seconddirection are disposed on the second surface of the first dielectriclayer, and wherein the second direction is different to the firstdirection, and bonding the second face of the first dielectric layer tothe first face of the transparent substrate. The method includesproviding a layer of piezoelectric material having first and secondfaces, and bonding the second face of the layer of piezoelectricmaterial to the first face of the first dielectric layer. The methodincludes providing a second dielectric layer having first and secondopposite faces, wherein a third conductive material region is disposedon the second face of the second dielectric layer such that, whenassembled, the third conductive region at least partially overlaps eachfirst conductive region and each second conductive region, and bondingthe second face of the second dielectric layer to the first face of thelayer of piezoelectric material. Each first conductive region comprisesa continuous conductive region and each second conductive regioncomprises a plurality of separate conductive regions connected byjumpers, each jumper spanning a portion of a first conductive region.

According to a fifteenth aspect of the invention there is provided amethod of fabricating a layer structure for a touch panel. The methodincludes providing a transparent substrate having first and secondopposite faces, wherein a plurality of first conductive regionsextending in a first direction and spaced apart perpendicular to thefirst direction are disposed on the first face of the glass sheet,providing a first dielectric layer having first and second oppositefaces, wherein a plurality of second conductive regions extending in asecond direction and spaced apart perpendicular to the second directionare disposed on the second surface of the first dielectric layer, andwherein the second direction is different to the first direction, andbonding the second face of the first dielectric layer to the first faceof the transparent substrate. The method includes providing a layer ofpiezoelectric material having first and second opposite faces, andbonding the second face of the layer of piezoelectric material to thefirst face of the first dielectric layer. The method includes providinga second dielectric layer having first and second opposite faces,wherein a third conductive material region is disposed on the secondface of the second dielectric layer such that, when assembled, the thirdconductive region at least partially overlaps each first conductiveregion and each second conductive region, and bonding the second face ofthe second dielectric layer to the first face of the layer ofpiezoelectric material.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the present invention will now be described, byway of example, with reference to the accompanying drawings in which:

FIG. 1 schematically illustrates a first apparatus including a firsttouch sensor and a front end module for combined capacitive and pressuresensing;

FIG. 2 schematically illustrates a second apparatus including a secondtouch sensor;

FIG. 3 is a block diagram of an electronic device;

FIG. 4 illustrates the operation of the front end module shown in FIG.1;

FIG. 5 illustrates the operation of the front end module shown in FIG. 1using a single ended amplifier;

FIG. 6 illustrates the operation of the front end module shown in FIG. 1using a differential amplifier;

FIG. 7 schematically illustrates an example of a filter configurationfor the front end module shown in FIG. 1;

FIG. 8 schematically illustrates an example of a filter configurationfor the front end module shown in FIG. 1;

FIG. 9 schematically illustrates an example of a filter configurationfor the front end module shown in FIG. 1;

FIG. 10 is a schematic circuit diagram of a first amplifier included inthe apparatus shown in FIG. 1;

FIG. 11 is a schematic circuit diagram of the first amplifier shown inFIG. 10 included in the apparatus shown in FIG. 2;

FIG. 12 is a schematic circuit diagram of a second amplifier included inthe apparatus shown in FIG. 1;

FIG. 13 is a schematic circuit diagram of a third amplifier included inthe apparatus shown in FIG. 1;

FIG. 14 is a schematic circuit diagram of a fourth amplifier included inthe apparatus shown in FIG. 1;

FIG. 15 is a cross-sectional view of a first touch panel for combinedcapacitive and pressure sensing;

FIG. 16 schematically illustrates a third apparatus including the touchpanel shown in FIG. 15;

FIG. 17 is a schematic circuit diagram of the first amplifier shown inFIG. 10 included in the apparatus shown in FIG. 16;

FIG. 18 is a schematic circuit diagram of the second amplifier shown inFIG. 12 included in the apparatus shown in FIG. 16;

FIG. 19 is a plan view of a patterned electrode for the touch panelshown FIG. 15;

FIG. 20 illustrates using interpolation based on measured pressurevalues to estimate a location and a pressure of a user interaction witha touch panel;

FIG. 21 is a cross-sectional view of a second touch panel for combinedcapacitive and pressure sensing;

FIG. 22 schematically illustrates a fourth apparatus including the touchpanel shown in FIG. 21;

FIG. 23 is a plan view of an arrangement of electrodes for the touchpanel for combined capacitive and pressure sensing shown in FIG. 21;

FIG. 24 is a plan view of an arrangement of electrodes for a third touchpanel for combined capacitive and pressure sensing;

FIG. 25 schematically illustrates a fifth apparatus including the touchpanel shown in FIG. 21;

FIG. 26 is a schematic circuit diagram of the first amplifier shown inFIG. 10 included in the apparatus shown in FIG. 25;

FIG. 27 is a cross-sectional view of a fourth touch panel for combinedcapacitive and pressure sensing;

FIG. 28 schematically illustrates a sixth apparatus including the touchpanel shown in FIG. 27;

FIG. 29 is a schematic circuit diagram of the third amplifier shown inFIG. 13 included in the apparatus shown in FIG. 28;

FIGS. 30A to 30C illustrate a first display stack-up at different stagesduring fabrication;

FIGS. 31A to 31C illustrate a second display stack-up at differentstages during fabrication;

FIGS. 32A to 32C illustrate a third display stack-up at different stagesduring fabrication;

FIGS. 33A to 33D illustrate a fourth display stack-up at differentstages during fabrication;

FIGS. 34A and 34B illustrate a fifth display stack-up at differentstages during fabrication;

FIGS. 35A and 35B illustrate a sixth display stack-up at differentstages during fabrication;

FIGS. 36A to 36C illustrate a seventh display stack-up at differentstages during fabrication;

FIGS. 37A to 37D illustrate an eighth display stack-up at differentstages during fabrication;

FIG. 38 illustrates a first embedded display stack-up;

FIG. 39 illustrates a second embedded display stack-up;

FIG. 40 illustrates a third embedded display stack-up;

FIG. 41 illustrates a fourth embedded display stack-up;

FIG. 42 illustrates a fifth embedded display stack-up;

FIG. 43 illustrates a sixth embedded display stack-up;

FIG. 44 illustrates a seventh embedded display stack-up;

FIG. 45 illustrates an eighth embedded display stack-up;

FIG. 46 is a plan view of an arrangement of electrodes for a fifth touchpanel for combined capacitive and pressure sensing; and

FIG. 47 is a cross-sectional view of the touch panel shown in FIG. 46.

DETAILED DESCRIPTION

In the following description, like parts are denoted by like referencenumerals.

First Combined Capacitance and Pressure Sensing Apparatus and FirstTouch Sensor:

FIG. 1 schematically illustrates a first apparatus 1 for combinedcapacitive and pressure sensing which includes a first touch sensor 2, afront end module 3, and a first signal processing module 4.

The first touch sensor 2 includes a layer structure 5 having a firstface 6 and a second, opposite, face 7, a first electrode 8 and a secondelectrode 9. The layer structure 5 includes one or more layers,including at least a layer of piezoelectric material 10. Each layerincluded in the layer structure 5 is generally planar and extends infirst x and second y directions which are perpendicular to a thicknessdirection z. The one or more layers of the layer structure 5 arearranged between the first and second faces 6, 7 such that the thicknessdirection z of each layer of the layer structure 5 is perpendicular tothe first and second faces 6, 7. The first electrode 8 is disposed onthe first face 6 of the layer structure 5, and the second electrode 9 isdisposed on the second face 7 of the layer structure 5. The firstelectrode 8 is electrical coupled to a terminal A and the secondelectrode 9 is coupled to a terminal B.

Preferably, the piezoelectric material is a piezoelectric polymer suchas polyvinylidene fluoride (PVDF). However, the piezoelectric materialmay alternatively be a layer of a piezoelectric ceramic such as leadzirconate titanate (PZT). Preferably, the first and second electrodesare indium tin oxide (ITO) or indium zinc oxide (IZO).

However, the first and second electrodes 8, 9 may be metal films such asaluminium, copper, silver or other metals suitable for deposition andpatterning as a thin film. The first and second electrodes 8, 9 may beconductive polymers such as polyaniline, polythiphene, polypyrrole orpoly(3A-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS). Thefirst and second electrodes may be formed from a metal mesh; nanowires,optionally silver nanowires; graphene; and carbon nanotubes.

The front end module 3 is coupled to the first touch sensor 2 viaterminal A in order to receive an input signal 11 from the firstelectrode 8. The front end module includes a first stage 12 in the formof an amplification stage, and a second stage in the form of a firstfrequency-dependent filter 13 and a second frequency-dependent filter14. The first stage 12 receives the input signal 11 from the firstelectrode 8, and provides an amplified signal 15 based on the inputsignal 11. The first frequency-dependent filter 13 receives and filtersthe amplified signal 15 to provide a first filtered signal 16 having afirst frequency bandwidth. The second frequency-dependent filter 14receives and filters the amplified signal 15 to provide a secondfiltered signal 17 having a second frequency bandwidth. The frequencybandwidth has a relatively higher start-frequency than the firstfrequency bandwidth.

The input signal 11 is produced in response to a user interaction withthe touch sensor 2 or with a layer of material overlying the touchsensor 2. In the following description, reference to a “userinteraction” shall be taken to include a user touching or pressing atouch sensor, a touch panel or a layer of material overlying either. Theterm “user interaction” shall be taken to include interactions involvinga user's digit or a stylus (whether conductive or not). The term “userinteraction” shall also be taken to include a user's digit or conductivestylus being proximate to a touch sensor or touch panel without directphysical contact.

The terminal B may couple the second electrode 9 to ground, to a voltagebias source 52 (FIG. 10) providing a constant potential, to a signalsource 44 providing a periodic signal 43 or to the front end module 3such that the front end module 3 is connected across the terminals A andB.

The terminals A, B, and other terminals denoted herein by capitalisedLatin letters are used as reference points for describing electricalcoupling between electrodes and other elements of an apparatus. Althoughthe terminals A, B may actually be physical terminals, the descriptionthat an element, for example a front end module 3, is coupled to aterminal, for example, the terminal A shall be taken to mean that thefront end module is directly coupled to the first electrode 8. Similarlyfor other elements and other terminals denoted by capitalised Latinletters.

The first signal processing module 4 receives the first and secondfiltered signals 16, 17. The first signal processing module 4 calculatespressure values 18 based on the first filtered signal 16 and capacitancevalues 19 based on the second filtered signal 17. The pressure values 18depend upon a deformation, which may be a strain, applied to the layerof piezoelectric material and corresponding to a user interaction. Thecapacitance values 19 depend upon the self-capacitance of the firstelectrode 8 and/or a mutual capacitance between the first and secondelectrodes 8, 9. The capacitance values 19 vary in response to a userinteraction involving a digit or a conductive stylus.

In this way, pressure and capacitance measurements may be performedusing the touch sensor 2 without the need for separate pressure andcapacitance electrodes. A single input signal 11 is received from thefirst electrode 8 which includes pressure and capacitance information.Additionally, the input signal 11 may be amplified and processed using asingle front end module 3. This can allow the apparatus 1 to be morereadily integrated into existing projected capacitance touch panels.

The layer structure 5 may include only the layer of piezoelectricmaterial 10, such that the first and second opposite faces 6, 7 arefaces of the piezoelectric material layer to (FIGS. 15, 21, 27, 32 and38). Alternatively, the layer structure 5 may include one or moredielectric layers which are stacked between the layer of piezoelectricmaterial 1 to and the first face 6 of the layer structure 5 (FIGS. 31,33, 35 and 36). The layer structure 5 may include one or more dielectriclayers stacked between the second face 7 of the layer structure 5 andthe layer of piezoelectric material 10 (FIG. 33). Preferably, one ormore dielectric layer(s) include layers of a polymer dielectric materialsuch as polyethylene terephthalate (PET), or layers of pressuresensitive adhesive (PSA) material. However, one or more dielectriclayer(s) may include layers of a ceramic insulating material such asaluminium oxide.

In FIG. 1, the first and second faces 6, 7 and the layers of the layerstructure 5 are shown extending along orthogonal axes labelled x and y,and the thickness direction of each layer of the layer structure 5 isaligned with an axis labelled z which is orthogonal to the x and y axes.However, the first, second and thickness directions need not form aright handed orthogonal set as shown. For example, the first and seconddirections x, y may intersect at an angle of 30 degrees or 45 degrees orany other angle greater than 0 degrees and less than 90 degrees.

Second Combined Capacitance and Pressure Sensing Apparatus and SecondTouch Sensor:

Referring also to FIG. 2, a second apparatus 20 is shown which includesa second touch sensor 21, a first front end module 3 a, a second frontend module 3 b and a second signal processing module 22.

The second touch sensor 21 is similar to the first touch sensor 2,except that the second touch sensor 21 also includes a second layerstructure 23 having a third face 24 and a fourth, opposite, face 25, anda third electrode 26. The second layer structure 23 includes one or moredielectric layers 27. Each dielectric layer 27 is generally planar andextends in first x and second y directions which are perpendicular to athickness direction z. The one or more dielectric layers 27 of thesecond layer structure 23 are arranged between the third and fourthfaces 24, 25 such that the thickness direction z of each dielectriclayer 27 of the second layer structure 23 is perpendicular to the thirdand fourth faces 24, 25. The third electrode 26 is disposed on the thirdface 24 of the second layer structure 23, and the fourth face 25 of thesecond layer structure 23 contacts the first electrode 8.

Preferably, the dielectric layer(s) 27 include layers of a polymerdielectric material such as PET or layers of PSA materials. However, thedielectric layer(s) 27 may include layers of a ceramic insulatingmaterial such as aluminium oxide. Preferably, the third electrode 26 ismade of indium tin oxide (ITO) or indium zinc oxide (IZO). However, thethird electrode 26 may be a metal mesh film such as aluminium, copper,silver or other metals suitable for deposition and patterning as a thinfilm. The third electrode 26 may be made of a conductive polymer such aspolyaniline, polythiphene, polypyrrole orpoly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS).

The first and second front end modules 3 a, 3 b are the same as thefront end module 3. The first front end module 3 a is coupled to thesecond touch sensor 21 via a terminal D in order to receive a firstinput signal 11 a from the first electrode 8. The second front endmodule 3 b is coupled to the second touch sensor 21 via a terminal C inorder to receive a second input signal 11 b from the third electrode 26.A terminal E may couple the second electrode 9 to ground, to a voltagebias source 52 (FIG. 10) providing a constant potential, or to a signalsource 44 providing a periodic signal 43. Alternatively, the terminal Emay be coupled to the first front end module 32 a such that the firstfront end module 3 a is connected across the terminals D and E, and theterminal E may also be coupled to the second front end module 3 b suchthat the second front end module 3 b is connected across the terminals Cand E.

The second signal processing module 22 receives first and secondfiltered signals 16 a, 17 a from the first front end module 32 a andfirst and second filtered signals 16 b, 17 b from the second front endmodule 3 b. The second signal processing module 22 calculates firstpressure values 18 a and capacitance values 19 a based on the filteredsignals 16 a, 17 a from the first front end module 3 a and the secondfiltered signal 17 b from the second front end module 3 b. The secondsignal processing module 22 calculates second pressure values 18 b andcapacitance values 19 b based on the filtered signals 16 b, 17 b fromthe second front end module 3 b and the second filtered signal 17 a fromthe first front end module 3 a. The pressure values 18 a, i 8 b dependupon a deformation applied to the layer of piezoelectric material to bya user interaction. The first capacitance values 19 a depend upon theself-capacitance of the first electrode 8 and/or a mutual capacitancebetween the first and second electrodes 8, 9 and/or upon a mutualcapacitance between the first and third electrodes 8, 23. The secondcapacitance values 19 b depend upon the self-capacitance of the thirdelectrode 26 and/or a mutual capacitance between the third and secondelectrodes 23, 9, and/or upon a mutual capacitance between the first andthird electrodes 8, 23. The capacitance values 19 vary in response to auser interaction involving a digit or a conductive stylus.

The second layer structure 23 may include only a single dielectric layer27, such that the third and fourth opposite faces 24, 25 are faces of asingle dielectric layer 27 (FIGS. 21, 23, 30, 34, 36). Alternatively, asecond layer structure need not be used, and the third electrode 26could be disposed on the first face 6 along with the first electrode 8(FIGS. 24, 35, 37). In FIG. 2, the third and fourth faces 24, 25 and thedielectric layers 27 of the second layer structure 23 are shownextending along orthogonal axes labelled x and y, and the thicknessdirection of each dielectric layer 23 of the second layer structure 23is aligned with an axis labelled z which is orthogonal to the x and yaxes. However, the first, second and thickness directions need not forma right handed orthogonal set as shown.

Electronic Device:

Referring also to FIG. 3, an electronic device 28 may include a touchpanel 29 and a touch controller 30 for providing combined capacitive andpressure sensing.

The electronic device 28 may be a relatively immobile electronic devicesuch as, for example a desktop computer, an automated teller machine(ATM), a vending machine, a point of sale device, or a public accessinformation terminal. Alternatively, an electronic device 28 may be aportable electronic device such as a laptop, notebook or tabletcomputer, a mobile phone, a smart phone, a personal data assistant or amusic playing device. The electronic device 28 includes a touch panel 29including one or more touch sensors 2, 21. The touch panel 29 is coupledto a touch controller 30 including one or more front end modules 3 by alink 31. In a case where the link 31 is a multiplexed link, one frontend module 3 may receive input signals 11 from multiple touch sensors 2,21. For example, using a multiplexed link 31 the touch controller 30 mayinclude one front end module and the touch panel 29 may include two,four, eight, sixteen, thirty two, sixty four, one hundred and twentyeight, two hundred and fifty six or more touch sensors 2, 21. The numberof touch sensors 2, 21 coupled to a front end module 3 by a multiplexedlink 31 need not be a power of two.

The electronic device 28 may include a processor 32 for executingprograms and processing information. The electronic device 28 mayinclude a memory 33 such as a volatile random access memory fortemporarily storing programs and information, and/or storage 31 such asnon-volatile random access memory (NVRAM) or a hard disc drive (HDD) forlong term storage of programs and information. The electronic device 28may include a network interface 35 for transmitting and/or receivinginformation from wired or wireless communication networks. Theelectronic device 28 may include a removable storage interface 36 whichcan interface with removable storage media to read and/or write programsand information. The electronic device 28 may include output means suchas a display 37 and/or speaker(s) 38. The display 37 may be any type ofdisplay such as, for example, an liquid crystal display (LCD), a lightemitting diode display (LED), an organic LED display, an electrophoreticdisplay or other type of electronic-ink display.

The touch controller 30 provides input information to the electronicdevice 28 which corresponds to user interactions with the touch panel29. For example, input information may be the locations and/or pressuresof one or more user interactions. The electronic device may includeother input means such as a microphone 39, or other input devices 40such as, for example, a keyboard, keypad, mouse or trackball. When thetouch panel 29 includes a plurality of touch sensors 2, 21, the touchcontroller 30 may provide positional information in the form ofcoordinates and/or pressures corresponding to one or more simultaneoususer interactions with the touch panel 29.

The touch panel 29 may be provided overlying the display 37, such thatthe touch panel 29 and display 37 provide a touch screen. Alternatively,the touch sensors 2, 21 of the touch panel 29 may be integrated into orembedded within the display 37. When the touch panel 29 is usedoverlying or integrated into the display 37, the layer structure(s) 5,23 and electrodes 8, 9, 26 may be transparent or substantiallytransparent. For example, the layer structure(s) 5, 23 and electrodes 8,9, 26 may transmit 50% or more, preferably at least 75%, preferably atleast 90% of light in visible wavelengths. For example, thepiezoelectric material may be PVDF, dielectric layers included in thelayers structures 5, 23 may be PET or an optically clear PSA, and theelectrodes 8, 9, 26 may be ITO. Alternatively, the electrodes 8, 9, 26,and any connections thereto, may be opaque and sufficiently thin in adirection perpendicular to the thickness direction z that they are notimmediately noticeable to the human eye, for example, electrodes, andany connections thereto, may be less than 100 micrometers (1×10⁻⁴ m)wide, less than 10 micrometers (1×10⁻⁵ m) wide or thinner.

Operation of the First and Second Apparatuses:

Referring also to FIG. 4, operation of the first end module 3 will beexplained.

The layer of piezoelectric material to is poled such that a polarisationP of the layer of piezoelectric material 10 having a component P_(z) inthe thickness direction z will be generated by the application of apressure (or stress or force) in the thickness direction z which resultsfrom a user interaction with the touch sensor 2, 21. The polarisation Pof the layer of piezoelectric material results in an induced electricfield E_(p), which has a component E_(p) in the thickness direction.Preferably, the layer of piezoelectric material 10 is poled such thatthe induced electric field E_(p) is orientated substantially in thethickness direction z, such that the component of the induced electricfield E_(p) in the thickness direction E_(x) is substantially largerthan any components perpendicular to the thickness direction E_(x),E_(y). Preferably, the induced electric field E_(p) is orientated at anangle within 10 degrees of the thickness direction z. However, theinduced electric field E_(p) may be orientated at an angle within 30degrees, within 45 degrees or within 60 degrees of the thicknessdirection z. The deformation which produces the polarisation P mayresult from a compression or a tension. The deformation which producesthe polarisation P may be an in-plane stretching of the piezoelectricmaterial layer 10.

The induced electric field E_(p) produces a potential difference betweenthe first and second electrodes 8, 9 of the first or second touchsensors 2, 21. The induced electric field E_(p) produces a potentialdifference between the third and second electrodes 26, 9 of the secondtouch sensor 21. If a conductive path is provided between the first orthird electrodes 8, 26 and the second electrode 9, charges will flowbetween them until the induced electric field E_(p) is cancelled by anelectric field E_(q) produced by the charging of the electrodes 8, 9,26. Intimate contact between the layer of piezoelectric material to andthe electrodes 8, 9, 26 is not required, provided that interveninglayers of the layer structures 5, 23 are not so thick that the inducedelectric field E_(p) is negligible at the location of an electrode 8, 9,26. A potential difference may be produced between the third and secondelectrodes 23, 9 of the second touch sensor 21 provided that the firstelectrode 8 is arranged such that the third electrode 23 is not entirelyscreened from the induced electric field E_(p).

The input signal 11 received from the first electrode 8 or the thirdelectrode 23 includes a current signal I_(piezo)(t) which depends uponthe induced electric field E_(p) (because there exists a finiteresistance between the first or third electrodes 8, 26 and the secondelectrode 9). Generally, a greater deformation applied to the layer ofpiezoelectric material to will result in a greater induced electricfield E_(p) and a correspondingly larger magnitude of I_(piezo)(t). Thefirst stage 12 includes a circuit providing an integrating amplifierwhich integrates the current signal I_(piezo)(t) and multiplies by again G in order to provide an integrated output voltage signalV_(piezo)(t). The gain G need not be fixed, and in general may be by afunction of time, frequency and/or the electrical parameters of afeedback network included in the first stage 12. The current signalI_(piezo)(t) and leakage currents result in the magnitude of the inducedelectric field E_(p) decaying slowly over time (also referred to hereinas “rolling off”) in response to a static pressure applied by a user.For example, when a user presses the touch sensor 2, 21 the integratedoutput voltage signal V_(piezo)(t) will display a rapidly rising period41, followed by a relatively slowly decaying period 42.

The amplified signal 15 is a superposition of the integrated outputvoltage signal V_(piezo)(t) and a capacitance measurement voltage signalV_(cap)(t). The capacitance voltage signal V_(cap)(t) is a periodicsignal having a basic frequency of f_(d). The capacitance voltage signalV_(cap)(t) is based on the capacitance of the touch sensor 2, 21 and aperiodic signal 43 provided by a signal source 44. Relative to theperiodic signal 43, one or more of the amplitude, phase or frequency ofthe capacitance voltage signal V_(cap)(t) depends directly upon thecapacitance of the touch sensor 2, 21.

For the first touch sensor 2, a signal source 44 may be coupled to thefront end module 3 or to the second electrode 9 via terminal B. For thesecond touch sensor 21, signal source(s) 44 may be coupled to the firstand second front end modules 3 a, 3 b or to the second electrode 9 viaterminal E. The signal source 44 may be a voltage controlled sourceV_(d)(f_(d)) or a current controlled source I_(d)(f_(d)). When thesignal source 44 is a current controlled source I_(d)(f_(d)) and theperiodic signal 43 is an input to the front end modules 3 a, 3 b of thesecond apparatus 20, a pair of synchronised current controlled sourcesI_(d)(f_(d)) are used so that current drawn by one front end module 3 a,3 b does not disturb the periodic signal 43 supplied to the other.

The signal source 44 may provide a periodic signal 43 having asinusoidal, square, triangular or saw-toothed waveform. The signalsource may provide a periodic signal comprising a superposition of twoor more sinusoidal waveforms having different frequencies.

Preferably, the front end module 3 receives the periodic signal 43 andthe first stage 12 provides the amplified signal 15 based on the inputsignal 11 and the periodic signal 43. The amplified signal 15 is asuperposition of the integrated output voltage signal V_(piezo) (t) andthe capacitance measurement voltage signal V_(cap)(t). However, theintegrated output voltage signal V_(piezo)(t) and the capacitancemeasurement voltage signal V_(cap)(t) generally have distinctlydifferent frequency contents, which facilitates separation using thefirst and second frequency-dependent filters 13,14. Where a userinteraction does not apply a pressure to the layer of piezoelectricmaterial the contribution of the integrated output voltage signalV_(piezo)(t) to the amplified signal 15 may be zero or negligible.

Self capacitances of the first or third electrodes 8, 26, or mutualcapacitances between any pair of the first, second or third electrodes8, 9, 26 may typically fall within the range of 0.1 to 3000 pF or more,and preferably 100-2500 pF. In order to effectively couple tocapacitances in this range, the periodic signal 43 may typically have abase frequency of greater than or equal to 10 kHz, greater than or equalto 20 kHz, greater than or equal to 50 kHz or greater than or equal to100 kHz. The periodic signal 43 may be provided with a narrow frequencyband or may be provided by a single frequency signal, such as asinusoidal signal.

By contrast, the integrated output voltage signal V_(piezo)(t) typicallyincludes a broadband frequency content spanning a range from several Hzto several hundreds or thousands of Hz. This is partly because theintegrated output voltage signal V_(piezo)(t) arises from userinteractions by a human user and partly because of the slowly decayingroll off period 42.

Preferably, the first frequency-dependent filter 13 attenuates thecapacitance measurement voltage signal V_(cap)(t) such that the firstfiltered signal 16 is not based on the periodic signal 43. Preferably,the first filtered signal 16 is substantially equal to the integratedoutput voltage signal V_(piezo)(t).

Preferably, the second frequency-dependent filter 14 selects thecapacitance measurement voltage signal V_(cap)(t) such that the secondfiltered signal 17 is based on the periodic signal 43 and thecapacitance of the touch sensor 2, 21. Preferably, the second filteredsignal 17 is substantially equal to the capacitance measurement voltagesignal V_(cap)(t). Preferably, the first stage 12 provides the amplifiedsignal 15 such that the amplitude of the capacitance measurement voltagesignal V_(cap)(t) depends upon the capacitance of the touch Sensor 2,21.

In this way, the amplitude of the first filtered signal 16 is dependentupon a pressure applied to the layer of piezoelectric material 10 by auser interaction, and the amplitude of the second filtered signal 17 isdependent upon a capacitance of a the touch sensor 2, 21 as modified bya user interaction.

Referring also to FIG. 5, a change in amplitude of the second filteredsignal 17 in response to a user interaction in a case where the firststage 12 uses a single ended amplifier circuit is shown.

When there is no user interaction with a touch sensor 2, 21, the secondfiltered signal 17 has a baseline amplitude V_(o). In response to a userinteraction with the touch sensor 2, 21, the amplitude of the secondfiltered signal changes to V_(cap), which may be greater than, less thanor equal to V_(o), depending on the configuration of the first stage 12.The user interaction is detected by the change in the amplitudeV_(o)−V_(cap) of the second filtered signal 17.

Referring also to FIG. 5, a change in amplitude of the second filteredsignal 17 in response to a user interaction in a case where the firststage 12 uses a differential amplifier circuit is shown.

When there is no user interaction with a touch sensor 2, 21, the secondfiltered signal 17 has a baseline amplitude V_(o) which is zero,negligible or as small as possible. In response to a user interaction,the amplitude of the second filtered signal changes to V_(cap), which isgreater than V_(o). In the same way as the case using a single endedamplifier, the user interaction is detected by the change in amplitudeV_(o)− V_(cap) of the second filtered signal 17. However, in a casewhere the first stage 12 uses a differential amplifier circuit, it maybe possible to increase the sensitivity of the first stage 12amplification without requiring an analog to digital converter with avery high dynamic range in order to digitise and further process thesecond filtered signal 17.

Referring also to FIGS. 7 to 9, the frequency-attenuation behaviour ofthe first stage 12, and the second stage including the first and secondfrequency-dependent filters 13, 14 are shown.

The first stage 12 has a frequency response 45 having a low frequencycut-off f_(i) and a high frequency cut-off f_(u). Below the lowfrequency cut-off f_(i) and above the high frequency cut-off f_(u) thegain G of the first stage drops rapidly so that frequencies outside therange f_(i) to f_(u) are blocked. The high frequency cut-off f_(u) isgreater than the base frequency f_(d) of the periodic signal 43. Thelow-frequency cut-off is preferably at least 1 hertz, or at leastsufficiently high to substantially block voltage signals resulting froma pyroelectric effect in the layer of piezoelectric material 10 whichresult from the body temperature of a user's digit. For application inan industrial or domestic environment, the low frequency cut-off f_(i)may be at least 50 Hz, at least 60 Hz or at least sufficiently high toreject noise pick-up at a frequency of a domestic of industrial powerdistribution network and resulting from ambient electric fields. The lowfrequency cut-off f may be at least 100 Hz. The low frequency cut-offf_(i) may be at least 200 Hz. For application in aircraft, the lowfrequency cut-off f_(i) may be at least 400 Hz.

Referring in particular to FIG. 7, the first frequency-dependent filter13 may be a low-pass filter 46 having a cut-off frequency f_(off) whichis lower than the base frequency f_(d) of the periodic signal 43, andthe second frequency-dependent filter 14 may be a band-pass filter 47having a pass-band including the base frequency f_(d).

Referring in particular to FIG. 8, the first frequency-dependent filter13 may be a band-reject filter 48 having a stop-band including the basefrequency f_(d), and the second frequency-dependent filter 14 may be aband-pass filter 47 having a pass-band including the base frequencyf_(d).

Referring in particular to FIG. 9, the first frequency-dependent filter13 may be a low-pass filter 46 having a cut-off frequency f_(off) whichis lower than the base frequency f_(d) of the periodic signal 43, andthe second frequency-dependent filter 14 may be a high-pass filter 49having a cut-off frequency f_(on) which is lower than the base frequencyf_(d) of the periodic signal 43 and higher than the cut-off frequencyf_(off) of the first frequency-dependent filter 13.

The band-pass filter 47 and/or the band-reject filter 48 may be notchfilters or comb filters. If the periodic signal 43 has a sinusoidalwaveform the band-pass filter 47 and/or the band-reject filter 48 arepreferably notch filters centred at the base frequency f_(d). If theperiodic signal 43 has a non-sinusoidal waveform, then the band-passfilter 47 and/or the band-reject filter 48 are preferably wideband-filters or comb-filters having pass/reject bands centred at thebase frequency f_(d) and harmonics thereof.

The first and second frequency-dependent filters 13, 14 may be providedby active filter circuits. The first and second frequency-dependentfilters 13, 14 may be provided by passive filter circuits. The first andsecond frequency-dependent filters 13, 14 may be provided by singlestage filters or multiple stage filters. The first and secondfrequency-dependent filters 13, 14 may be Butterworth filters, Chebyshevfilters, Gaussian filters and Bessel filters. The firstfrequency-dependent filter 13 may be of different type to the secondfrequency-dependent filter.

Alternatively, the second stage of the front end module 3 and the firstand second frequency-dependent filters 13, 14 may be provided by ansuitably programmed information processing device such as amicroprocessor or a microcontroller.

Examples of circuits which may provide the first stage 12 in cases wherethe periodic signal 43 is received by the front end module 3 shall nowbe described.

First Amplifier:

Referring also to FIG. 10, a first amplifier 50 for the first stage 12of the front end module 3 will be explained in a case where the signalsource 44 is a voltage controlled source V_(d)(f_(d)) which supplies theperiodic signal 43 to the front end module 3.

The first touch sensor 2 is represented in the circuit diagram by anequivalent circuit 51 in which C_(self) represents the self capacitanceof the first electrode 8, ΔC_(self) represents the change in the selfcapacitance of the first electrode resulting from the touch or proximityof a user's digit or a conductive stylus, C_(sensor) represents themutual capacitance between the first and second electrodes 8, 9 andP_(sensor) represents the piezoelectric response of the layer ofpiezoelectric material 10. The first electrode 8 is coupled to theterminal A and the second electrode 9 is coupled to a voltage biassource 52 which provides a constant bias voltage V_(bias) to the secondelectrode 9. The voltage bias V_(bias) may be a positive, negative orground potential.

The first amplifier 50 provides the first stage 12 of the front endmodule 3. The first amplifier 50 includes an operational amplifier OP1having at least an inverting input coupled to a first rail 53, anon-inverting input coupled to the voltage controlled sourceV_(d)(f_(d)) via a path 54 including a first resistor R_(d), and anoutput coupled to a second rail 55. The first amplifier 50 also includesa second resistor R_(i) coupling the first rail 53 to the terminal A. Inthis way, the first amplifier 50 is coupled to the first electrode 8.The first amplifier 50 also includes a third resistor R_(i) coupling thefirst rail 53 to the second rail 55, and a first capacitor C_(f)coupling the first rail 53 to the second rail 55. Optionally, a secondcapacitor C_(d) may be connected in parallel with the first resistorR_(d). Other terminals of the operational amplifier OP1, such as powersupply terminals, may be present but are not shown in this or otherschematic circuit diagrams described herein.

The gain and frequency dependence of the first amplifier 50 arecontrolled by the third resistor R_(f) and the first capacitor C_(f)which provide a negative feedback network to the operational amplifierOP1. In the first amplifier 50, the second rail 55 provides theamplified signal 15 via an output terminal V_(out). Alternatively, thesecond rail 55 may be directly coupled to the second stage of the frontend module 3.

Because the non-inverting input of the operational amplifier OP1 iscoupled to the voltage controlled source V_(d)(f_(d)), the amplifier iseffectively provided with a periodically varying virtual earth. In thisway, the amplified signal 15 output by the first amplifier 50 ismodulated by the periodic signal 43, and includes a superposition of theintegrated output voltage signal V_(piezo)(t) and the capacitancemeasurement voltage signal V_(cap)(t). One simple way to view theinteraction with the periodic signal 43 is using one of the “Goldenrules” of operational amplifiers, namely that when an ideal operationalamplifier is provided with a negative feedback network, the invertingand non-inverting inputs will be at the same potential. Thus, thepotential at the non-inverting input of the operational amplifier OP1varies with the periodic signal 43, and couples to the capacitances ofthe equivalent circuit 51. Coupling the periodic signal 43 to thecapacitances of the equivalent circuit 51 using the described virtualearth configuration may have the advantage of allowing higher gains tobe used to amplify the current signal I_(piezo)(t) without saturatingthe output of the operational amplifier OP1.

The capacitance of the first capacitor C_(f) may be selected to beapproximately equal to the mutual capacitance C_(sensor) between thefirst electrode 8 and the second electrode 9. The low frequency cut-offf_(i) of the first amplifier 50 may be approximated asf_(i)=1/(2π×R_(f)×C_(f)). The high frequency cut-off f_(u) may beapproximated as f_(u)=1/(2π×R_(i)×C_(f)). In this way, the second andthird resistors R_(i), R_(f) and the first capacitor C_(f) may beselected such that the high frequency cut-off f_(u) is greater than thebase frequency f_(d) of the periodic signal 43 and the low-frequencycut-off is at least 1 hertz or at least sufficiently high tosubstantially block voltage signals resulting from a pyroelectric effectin the layer of piezoelectric material to. Optionally, the low frequencycut-off f_(i) may be at least 50 Hz or at least 60 Hz or at leastsufficiently high to reject noise pick-up at a frequency of a domesticor industrial power distribution network.

The voltage bias source 52 need not provide a constant bias voltageV_(bias), and the voltage bias source 52 may instead provide a timevarying voltage. In some cases, the voltage bias source 52 mayalternatively be provided by the signal source 44 such that the periodicsignal 43 is provided to the second electrode 9.

The equivalent circuit 51 has been shown as including a variablecapacitance ΔC_(self) arising from self capacitance of the firstelectrode 8. However, the equivalent circuit 51 of the touch sensor 2may additionally or alternatively include a variable capacitanceΔC_(sensor) arising from a mutual capacitance between the first andsecond electrodes 8, 9. In general, the equivalent circuit 51 may bedifferent depending on the exact geometries of the first and secondelectrodes 8, 9 and the touch sensor 2.

Referring also to FIG. 11, the first amplifier 50 may provide the firststages 12 of the first and second front end modules 3 a, 3 b for thesecond apparatus 20.

A pair of first amplifiers 50 a, 50 b may provide the first stage of therespective front end modules 3 a, 3 b of the second apparatus 20 in asimilar way to the first apparatus 1. The input to a first amplifier 50a which is included in the first front end module 3 a is coupled viaterminal D to the first electrode 8 of the second touch sensor 21. Theinput to a first amplifier 50 b which is included in the second frontend module 3 b is coupled via terminal C to the third electrode 26 ofthe second touch sensor 21. The second electrode 9 of the second touchsensor 21 is coupled via terminal E to a voltage bias source 52. Thesame voltage controlled source 44, V_(d)(f_(d)) may be coupled to bothfront end modules 3 a, 3 b in parallel.

Thus, each first amplifier 50 a, 50 b provides a corresponding amplifiedsignal 15 a, 15 b depending upon input signals 11 a, 11 b from the firstand third electrodes 8, 26 respectively. One difference to the firsttouch sensor 2 is that the equivalent circuit 56 of the second touchsensor 21 also includes a mutual capacitance C_(mut) between the firstelectrode 8 and the third electrode 26.

Second Amplifier:

Referring also to FIG. 12, a second amplifier 57 for the first stage 12of the front end module 3 will be explained in a case where the signalsource 44 is a voltage controlled source V_(d)(f_(d)) which supplies theperiodic signal 43 to the front end module 3.

The first touch sensor 2 is represented in the circuit diagram by anequivalent circuit 51. The first electrode 8 is coupled to the terminalA and the second electrode 9 is coupled to a voltage bias source 52which provides a constant bias voltage V_(bias) to the second electrode9. The voltage bias V_(bias) may be a positive, negative or groundpotential.

The second amplifier 57 includes a first operational amplifier OP1having at least an inverting input coupled to a first rail 58, anon-inverting input coupled to the voltage controlled sourceV_(d)(f_(d)) via a path including a first resistor R_(d1) and a secondrail 59, and an output coupled to a third rail 60. The second amplifier57 includes a second operational amplifier OP2 having at least aninverting input coupled to a fourth rail 61, a non-inverting inputcoupled to the second rail 59 via a path including a second resistorR_(d2), and an output coupled to a fifth rail 62. The second amplifierincludes a comparator CM1 having at least an inverting input coupled tothe third rail 60, a non-inverting input coupled to the fifth rail 62,and an output providing the amplified signal 15. The second amplifier 57also includes a third resistor R_(i1) coupling the first rail 58 to theterminal A, a fourth resistor R_(f1) coupling the first rail 58 to thethird rail 60, a first capacitor C_(f1) coupling the first rail 58 tothe third rail 60, a fifth resistor R_(f2) coupling the fourth rail 61to the fifth rail 62, a second capacitor C_(f2) coupling the fourth rail61 to the fifth rail 62, and a sixth resistor R_(i2) coupling the fourthrail 61 to ground via a path 63 including a third capacitor C_(ref).

The first resistor R_(d1) may have a resistance substantially equal tothe second resistor R_(d2). The fourth resistor R_(f1) may have aresistance substantially equal to the fifth resistor R_(f2). The firstcapacitor C_(f1) may have a capacitance substantially equal to thesecond capacitor C_(f2), and also approximately equal to a mutualcapacitance C_(sensor) between the first electrode 8 and the secondelectrode 9. The third capacitor C_(ref) may have a capacitanceapproximately equal to a mutual capacitance C_(sensor) between the firstelectrode 8 and the second electrode 9. A fourth capacitor C_(d1) may beconnected in parallel with the first resistor R_(d1). A fifth capacitorC_(d2) may be connected in parallel with the second resistor R_(d2).

The second amplifier 57 operates in substantially the same way as thefirst amplifier 50, except that the second amplifier 57 is adifferential amplifier which ideally provides an amplified signal 15which has zero or negligible amplitude when there is no user interactionwith the touch sensor 2.

Referring also to FIGS. 2 and 11, the second amplifier 57 may be used inthe second apparatus 1 n the same way as the first amplifier 50 byconnecting the respective inputs of a pair of second amplifiers 57 tothe first and third electrodes 8, 26 of the second touch sensor 21 viathe terminals D and C respectively.

Third Amplifier:

Referring also to FIG. 13, a third amplifier 63 for the first stage 12of the front end module 3 will be explained in a case where the signalsource 44 is a current controlled source I_(d)(f_(d)) which supplies theperiodic signal 43 to the front end module 3.

The first touch sensor 2 is represented in the circuit diagram by theequivalent circuit 51. The first electrode 8 is coupled to the terminalA and the second electrode 9 is coupled to the terminal B. Both theterminal A and terminal B are coupled to the third amplifier 63.

The third amplifier 63 includes an operational amplifier OP1 having atleast an inverting input coupled to the current controlled sourceI_(d)(f_(d)) via a first rail 63, a non-inverting input coupled toground via a path 65 including a first resistor R_(d), and an outputcoupled to a second rail 66. The third amplifier 63 also includes asecond resistor (R_(f)) coupling the first rail 64 to the second rail66, and a third resistor R_(i) coupling the first rail 64 to ground viaa path including a first capacitor C_(f). In the third amplifier 63, thesecond rail 66 provides the amplified signal 15.

The first rail 64 is coupled to the first electrode 8 via terminal A andthe second rail 66 is coupled to the second electrode 9 via terminal B.Alternatively, the first rail 64 may be coupled to the second electrode9 via terminal B and the second rail 66 may be coupled to the firstelectrode 8 via terminal A.

A second capacitor C_(d) may be connected in parallel with the firstresistor R_(d). The first capacitor C_(f) may have a capacitancesubstantially equal to a mutual capacitance C_(sensor) between the firstelectrode 8 and the second electrode 9.

In many respects, for example the high and low frequency cut-offs f_(i),f_(u), the third amplifier 63 is configured similarly to the first andsecond amplifiers 50, 57. However, the feedback network of the thirdamplifier 63 differs from the first or second amplifiers 50, 57 becauseit includes the first touch sensor 2.

The second apparatus 20 may use front end modules 3 a, 3 b which havefirst stages 12 provided by the third amplifier 63. A third amplifier 63included in the first front end module 3 a may be connected across theterminals D and E instead of A and B, and a third amplifier 63 includedin the second front end module 3 b may be connected across the terminalsC and E. Optionally, a third front end module (not shown) may be usedwhich includes a third amplifier 63 connected across the terminals C andD. When more than one third amplifier 63 is used, each third amplifier63 should be coupled to the output of a separate, synchronised currentcontrolled source I_(d)(f_(d)).

Fourth Amplifier:

Referring also to FIG. 14, a fourth amplifier 67 for the first stage 12of the front end module 3 will be explained in a case where the signalsource 44 is a pair of synchronised current controlled sourcesI_(d1)(f_(d)), I_(d2)(f_(d)) which supply the periodic signal 43 to thefront end module 3.

The first touch sensor 2 is represented in the circuit diagram by theequivalent circuit 51. The first electrode 8 is coupled to the terminalA and the second electrode 9 is coupled to the terminal B. Both terminalA and terminal B are coupled to the third amplifier 63.

The fourth amplifier 67 includes a first operational amplifier OP1having at least an inverting input coupled to a first current controlledsource I_(d1)(f_(d)) via a first rail 68, a non-inverting input coupledto ground via a path 69 including a first resistor R_(d1), and an outputcoupled to a second rail 70. The fourth amplifier 67 also includes asecond operational amplifier OP2 having at least an inverting inputcoupled to a second current I_(d2)(f_(d)) source by a third rail 71, anon-inverting input coupled to ground via a path 72 including a secondresistor R_(d2), and an output coupled to a fourth rail 73. The fourthamplifier 67 also includes a comparator CM1 having at least an invertinginput coupled to the second rail 70, a non-inverting input coupled tothe fourth rail 73, and an output providing the amplified signal 15. Thefourth amplifier 67 also includes a third resistor R_(f1) coupling thefirst rail 68 and the second rail 70, a fourth resistor R_(i1) couplingthe first rail 68 to ground via a path including a first capacitorC_(f1), a fifth resistor R_(f2) coupling the third rail 71 to ground viaa path including a second capacitor C_(f2), a sixth resistor R_(f2)coupling the third rail 71 to the fourth rail 73, and a third capacitorC_(ref) coupling the third rail 71 to the fourth rail 73.

The first current controlled source I_(d2)(f_(d)) is synchronised withthe second current controlled source I_(d2)(f_(d)).

The first rail 68 is coupled to the first electrode 8 via terminal A andthe second rail 70 is coupled to the second electrode 9 via terminal B.Alternatively, the first rail 68 may be coupled to the second electrode9 via terminal B and the second rail 70 may be coupled to the firstelectrode 8 via terminal A.

The first resistor R_(d1) may have a resistance substantially equal tothe second resistor R_(d2). The third resistor R_(f1) may have aresistance substantially equal to the sixth resistor R_(f2). The firstcapacitor C_(f1) may have a capacitance substantially equal to thesecond capacitor C_(f2) and approximately equal to a mutual capacitanceC_(sensor) between the first electrode 8 and the second electrode 9. Thethird capacitor C_(ref) may have a capacitance approximately equal to amutual capacitance C_(sensor) between the first electrode 8 and thesecond electrode 9. A fourth capacitor C_(d1) may be connected inparallel with the first resistor R_(d1). A fifth capacitor C_(d2) may beconnected in parallel with the second resistor R_(d2).

The fourth amplifier 67 operates in substantially the same way as thethird amplifier 63, except that the fourth amplifier 67 is adifferential amplifier which ideally provides an amplified signal 15which has zero or negligible amplitude when user does not touch and/orpress the touch sensor 2.

The second apparatus 20 may use front end modules 3 a, 3 b which eachhave a first stage 12 provided by the fourth amplifier 67. A fourthamplifier 67 included in the first front end module 3 a may be connectedacross the terminals D and E instead of A and B as shown in FIG. 14, anda fourth amplifier 67 included in the second front end module 3 b may beconnected across the terminals C and E. Optionally, a third front endmodule (not shown) may be used which includes a fourth amplifier 67connected across the terminals C and D.

Third Combined Capacitance and Pressure Sensing Apparatus and FirstTouch Panel:

Referring also to FIGS. 15 and 16, a third apparatus 74 including afirst touch panel 29, a first touch controller 30 and a multiplexer 75will be explained.

The multiplexer 75 has a plurality of inputs and one output, the outputis coupled to a terminal F.

The first touch panel 29 includes a layer structure 5 which is generallythe same as the layer structure of the first touch sensor 2, except thatthe layer structure 5 of the first touch panel 29 is shared betweenmultiple first electrodes 8 disposed on the first face 6 in the form ofpads of conductive material. The first electrodes 8 are disposed on thefirst face 6 in an array extending in the first and second directions x,y. Each first electrode 8 is coupled to a corresponding input of themultiplexer 75 by a respective conductive trace 76. The conductivetraces 76 may be made of the same material as the first electrodes 8.Alternatively, the conductive traces 76 may be made of a material havinga higher conductivity than the material used for the first electrodes 8.The conductive traces 76 are generally much thinner in the plane definedby the first and second directions x, y than the corresponding firstelectrodes 8. The second electrode 9 is disposed on the second face 9and is extensive such that the second electrode at least partialunderlies each first electrode 8. The second electrode 9 may besubstantially coextensive with the second face 7. The second electrodeis coupled to a terminal G.

In this way, each first electrode 8 effectively provides a first touchsensor 2 which may be individually addressed using the multiplexer 75and the conductive traces 76.

The first touch panel 29 may be bonded overlying the display 37 of anelectronic device 28. In this case, the materials of the first touchpanel 29 should be substantially transparent as described hereinbefore.A cover lens 77 may be bonded overlying the first touch panel 29. Thecover lens 77 is preferably glass but may be any transparent material.The cover lens 77 may be bonded to the touch panel 29 using a layer ofPSA material 78. The layer of PSA material 78 may be substantiallytransparent. The array of first electrodes 8 and the correspondingconductive traces 76 may be fabricated using index matching techniquesto minimise visibility to a user.

The first touch controller 30 includes a front end module 3, a signalprocessing module 4 and a controller 79. The controller 79 maycommunicate with the processor 32 of the electronic device 28 using alink 80. The touch controller 30 may include a signal source 44providing the periodic signal 43 to the front end module 3

The front end module 3 is coupled to the output of the multiplexor 75 bythe terminal F. In this way, the front end module 3 may receive an inputsignal 11 from any one of the first electrodes 8 which is addressed bythe multiplexer 75. The front end module 3 may include a first stage 12provided by any one of the first, second, third or fourth amplifiers 50,57, 63, 67. Alternatively, the front end module 3 may include a firststage 12 using any circuit which provides an amplified signal 15 basedon the input signal 11 and including a superposition of the integratedoutput voltage signal V_(piezo)(t) and the capacitance measurementvoltage signal V_(cap)(t) as hereinbefore described.

In a case where the front end module 3 includes the first or secondamplifiers 50, 57, the second electrode 9 may be coupled to a biasvoltage source 52 via the terminal G. Alternatively, in a case when thefront end module 3 includes the third or fourth amplifiers 63, 67, thesecond electrode 9 may be coupled to the front end module 3 via theterminal G.

The controller 79 may provide a control signal 81 to the multiplexer 75.The control signal 81 may cause the multiplexer 75 to address each inputaccording to a sequence determined by the controller 79. In this way,the front end module 3 may receive an input signal 11 from each firstelectrode 8 according to a sequence determined by the controller 80. Thesequence may be pre-defined, for example, the sequence may select eachfirst electrode 8 once before repeating. The sequence may be dynamicallydetermined, for example, when one or more user interactions aredetected, the controller 79 may scan the subset of first electrodes 8adjacent to each detected user interaction in order to provide fasterand/or more accurate tracking of user touches. The sequence may bearranged so that the multiplexor 75 addresses each first electrode 8during a quiet period or blanking period of the display 37. The sequencemay be provided to the controller 79 by the processor 32 via the link80. Alternatively, the processor may directly control the sequence viathe link 80 .

In this way, the front end module 3 may receive input signals 11 fromeach of the first electrodes 8 which are disposed in an array extendingin the first and second directions. The signal processing module 4provides respective pressure values 18 and capacitance values 19 to thecontroller. The controller 79 uses the received pressure values 18 andcapacitance values 19 to calculate a position and an applied pressurefor one or more user interactions with the touch panel 29. Thecontroller 79 provides the positions and/or pressures of one or moreuser interactions to the processor 32 as input information via the link80. Alternatively, the pressure values 18 and capacitance values 19 maybe provided to the processor 32 via the link 80 and the processor 32 maycalculate the positions and/or pressures of one or more userinteractions. The controller 79 or the processor 32 are calibrated byapplying known pressures to known locations so that the accuracy ofcalculated positions and/or pressures of one or more user interactionsmay be optimised and/or verified.

Referring also to FIG. 17, a configuration of the first amplifier 50included in the third apparatus 74 is shown.

The configuration of the first amplifier 50 included in the thirdapparatus 74 is substantially the same as the configuration of the firstamplifier 50 included in the first apparatus 1, except that the firstrail 53 is coupled to the output of the multiplexor 75 via the terminalF instead of being coupled to the terminal A, the voltage bias source 52is coupled to the second electrode 9 via the terminal G instead of theterminal B, and that the first amplifier 50 further includes a switchSW1.

The switch SW1 is coupled between the first rail 53 and the second rail55 of the first amplifier 50. When the switch SW1 is closed, the firstcapacitor C_(f) of the first amplifier 50 is discharged. The opening andclosing of the switch SW1 may be governed by a control signal 82provided by the controller 79. In this way, after an input signal 11 hasbeen received from one of the first electrodes 8, the first capacitorC_(f) may be discharged in order to reset the feedback network of thefirst amplifier 50 before the multiplexer 75 addresses a different firstelectrode 8.

Referring also to FIG. 18, a configuration of the second amplifier 57included in the third apparatus 74 is shown.

The configuration of the second amplifier 57 included in the thirdapparatus 74 is substantially the same as the configuration of the firstamplifier 50 included in the third apparatus 74, except that the secondamplifier 57 is used instead of the first amplifier 50 and the secondamplifier 57 further includes a first switch SW1 and a second switchSW2.

The first switch SW1 couples the first rail 58 to the third rail 60 ofthe second amplifier 57 and the second switch SW2 couples the fourthrail 61 to the fifth rail 62. When the switch SW1 is closed, the firstcapacitor C_(f1) of the second amplifier 57 is discharged. When theswitch SW2 is closed, the second capacitor C_(f2) of the secondamplifier 57 is discharged. The opening and closing of the switches SW1,SW2 may be governed by control signals 82 provided by the controller 79.In this way, after an input signal 11 has been received from one of thefirst electrodes 8, the capacitors C_(f1), C_(f2) may be discharged soas to reset the feedback network of the second amplifier 57 before themultiplexer 75 addresses a different first electrode 8.

Alternatively, the third apparatus 74 may include the third amplifier63. In such a case, the first rail 64 of the third amplifier 63 may becoupled to the output of the multiplexor 75 via terminal F and thesecond rail 66 of the third amplifier 63 may be coupled to the secondelectrode 9 via terminal G. Alternatively, the first rail 64 of thethird amplifier 63 may be coupled to the second electrode 9 via terminalG and the second rail 66 of the third amplifier 63 may be coupled tooutput of the multiplexor 75 via terminal F.

Alternatively, the third apparatus 74 may include the fourth amplifier67. In such a case, the first rail 68 of the fourth amplifier 67 may becoupled to the output of the multiplexor 75 via terminal F and thesecond rail 70 of the fourth amplifier 67 may be coupled to the secondelectrode 9 via terminal G. Alternatively, the first rail 68 of thefourth amplifier 67 may be coupled to the second electrode 9 viaterminal G and the second rail 70 of the fourth amplifier 67 may becoupled to the multiplexor 75 via terminal F.

When a user interacts with the first touch panel 29 proximate to a givenfirst electrodes 8, the resulting change in capacitance of therespective touch sensor 2 formed by the given first electrode 8, thelocal region of the layer structure 5 and the local region of the secondelectrode 9, is mostly due to a change in the self-capacitance of thefirst electrode 8. This is because the magnitude of the mutualcapacitance C_(sensor) between the first electrode 8 and the secondelectrode 9 may be large such that a change in the mutual capacitance isrelatively small. The value of the mutual capacitance C_(sensor) betweenthe first electrode 8 and the second electrode 9 may be reduced ifrequired by using a patterned second electrode 9. Using a patternedsecond electrode 9 may allow the second electrode 9 to be disposedbetween a user's digit/stylus and the first and/or third electrodes 8,26 without screening electrostatic interactions between the user'sdigit/stylus and the first and/or third electrodes 8, 26.

Referring also to FIG. 19, a patterned second electrode 83 is in theform of a Cartesian grid. The conductive region of the patterned secondelectrode 83 includes struts 84 extending in the first direction x andhaving a width W in the second direction y, and struts 85 extending inthe second direction y and having a width W in the first direction x.The struts 84 extending in the first direction x are evenly spaced inthe second direction y with a spacing S, and the struts 85 extending inthe second direction y are evenly spaced in the first direction x withthe same spacing S. The struts 84, 85 are joined where they intersectsuch that the patterned second electrode 83 is formed of a single regionof conductive material.

The patterned second electrode 83 may be arranged such that themagnitude of the mutual capacitance C_(sensor) between the firstelectrode 8 and the second electrode 9 is reduced. This may increase therelative size of changes in the mutual capacitance ΔC_(sensor) betweenthe first electrode 8 and the second electrode 9 resulting from a user'stouch, making such changes ΔC_(sensor) easier to detect.

Referring also to FIG. 20, using pressure values to infer a locationand/or pressure of a user interaction occurring between two firstelectrodes 8 will be explained.

The separation between adjacent electrodes in a projected capacitancetouch panel, sometimes referred to as the pitch, may be relativelycoarse, for example, 1 to 5 mm or larger than 5 mm. If the positions ofuser interactions were determined only at the pitch length, projectedcapacitance touchscreens would not be able to provide accurate positionsof user interactions or to smoothly follow a path traced by a user. Toprovide more accurate locations, projected capacitance touchscreensemploy interpolation, for example, using an electrode having a peaksignal and also the adjacent electrode signals, in order to infer atouch location using linear interpolation, quadratic interpolation orinterpolation using higher order polynomials or other suitablefunctions. Such interpolation is possible because a user interaction mayalter the capacitances of several adjacent electrodes simultaneously.

Similarly, when a user presses on the cover lens 77, the layer ofpiezoelectric material 10 underlying the cover lens 77 will experiencestrain across a broader area because of the rigidity of the cover lens77. For example, a user interaction at a precise location 86 may resultin pressure values 87 a and 87 b being calculated for first electrodes 8at locations 88 a, 88 b which bracket the precise location 86. A userinteraction at a precise location 86 may also result in pressure values89 a and 89 b being calculated for first electrodes 8 at locations 90 a,90 b adjacent to the pair of bracketing locations 88 a, 88 b.

The controller 79 or the processor 32 may calculate an estimate of theprecise location 86 and/or a precise pressure value 91 using the largestvalue 87 a and the corresponding location 88 a in combination with thetwo next nearest values 87 b, 89 a and the corresponding locations 88 b,90 a. Alternatively, the controller 79 or the processor 32 may calculatean estimate of the precise location 86 and/or a precise pressure value91 using the pair of bracketing values 87 a, 87 b and locations 88 a, 88b. The controller 79 or the processor 32 may calculate an estimate ofthe precise location 86 and/or a precise pressure value 91 using thepair of bracketing values 87 a, 87 b and locations 88 a, 88 b and theadjacent values and locations 89 a, 89 n, 90 a, 90 b. The controller 79or the processor 32 may calculate an estimate of the precise location 86and/or a precise pressure value 91 using linear interpolation, quadraticinterpolation or interpolation using higher order polynomials or othersuitable functions.

The third apparatus 73 may operate using interpolation of capacitancevalues 19 and/or pressure values 18 to determine locations and pressuresof one or more user interactions.

Fourth Combined Capacitance and Pressure Sensing Apparatus and SecondTouch Panel:

Referring also to FIGS. 21 and 22, a fourth apparatus 93 including asecond touch panel 92, a first touch controller 300 and a multiplexer 75will be explained.

The fourth apparatus 93 is substantially the same as the third apparatus74, except that the fourth apparatus 93 includes a second touch panel 92instead of the touch panel 29.

The second touch panel 92 includes a layer structure 5 which isgenerally the same as the layer structure 5 of the second touch sensor21, except that in the touch panel 92, the layer structure 5 is sharedby multiple first electrodes 8 disposed on the first face 6 of the layerstructure 5, and the second layer structure 23 is shared by multiplethird electrodes 26 disposed on the third face 24 of the second layerstructure 23. The first electrodes 8 each extend in the first directionx and the first electrodes 8 are disposed in an array evenly spaced inthe second direction y. The third electrodes 26 each extend in thesecond direction y and the third electrodes 26 are disposed in an arrayevenly spaced in the first direction x. Each first electrode 8 and eachthird electrode 26 is coupled to a corresponding input of themultiplexer 75 by a respective conductive trace 76. The second electrode9 is disposed on the second face 9 and is extensive such that the secondelectrode at least partially underlies each first electrode 8 and eachthird electrode 26. The second electrode 9 may be substantiallycoextensive with the second face 7. The second electrode is coupled to aterminal G.

In this way, the area around each intersection of a first electrode 8with a third electrode 26 effectively provides a second touch sensor 21and each of the first and third 8, 26 electrodes may be individuallyaddressed using the multiplexer 75 and the conductive traces 76.

The second touch panel 92 may be bonded overlying the display 37 of anelectronic device 28 and a cover lens 77 may be bonded overlying thesecond touch panel 92 in the same way as for the touch panel 29.

The controller 79 may provide a control signal 81 to the multiplexer 75in the same way as for the third apparatus 74. However, in the fourthapparatus 93, the control signal 81 may cause the multiplexer 75 toaddress each input according to a different sequence to the thirdapparatus 74. For example, the control signal 81 may cause themultiplexer 75 to address a given first electrode 8, and to subsequentlyaddress each third electrode 26 intersecting the given first electrode 8before addressing a further first electrode 8 and repeating the scanthrough the third electrodes 26. The control signal 81 may cause themultiplexer to dynamically address first and third electrodes 8, 26proximate to first and third electrodes 8, 26 at which a user touch waspreviously detected.

In this way, a raster scan of the first and third electrodes 8, 26 maybe performed which allows the first touch controller 30 to determine thepositions and/or pressures of one or more user interactions.

In the similar way to the third apparatus 74, the changes in capacitancevalues 19 generated in the fourth apparatus 1 n response to userinteractions may be predominantly due to changes in self-capacitance ofthe addressed first or second electrode 8, 26. However, if a given pairof first and third electrodes 8, 26 are addressed sequentially andwithout excessive delay, a change in the mutual capacitance between thegiven pair of first and third electrodes 8, 26 may additionally bedetermined.

Although the first electrode 8 and the third electrode 26 have beenshown as being substantially rectangular, other shapes can be used.

Referring also to FIG. 23, an alternative arrangement of the first andthird electrodes 8, 26 is shown. Instead of being rectangular, eachfirst electrode 8 may include several pad segments 94 evenly spaced inthe first direction x and connected to one another in the firstdirection x by relatively narrow bridging segments 95. Similarly eachthird electrode 26 may comprise several pad segments 96 evenly spaced inthe second direction y and connected to one another in the seconddirection y by relatively narrow bridging segments 97. The pad segments94 of the first electrodes 8 are diamonds having a first width W3 in thesecond direction 7 and the bridging segments 95 of the first electrodes8 have a second width W2 in the second direction y. The pad segments 96and bridging segments 97 of the third electrodes 26 have the samerespective shapes and widths W1, W2 as the first electrodes 8.

The first electrodes 8 and the third electrodes 26 are arranged suchthat the bridging segments 97 of the third electrodes 26 overlie thebridging segments 95 of the first electrodes 8. Alternatively, the firstelectrodes 8 and the third electrodes 26 may be arranged such that thepad segments 96 of the third electrodes 26 overlie the pad segments 94of the first electrodes 8. The pad segments 94, 96 need not be diamondshaped, and may instead be circular. The pad segments 94, 96 may be aregular polygon such as a triangle, square, pentagon or hexagon. The padsegments 94, 96 may be I shaped or Z shaped.

Third Touch Panel:

Referring also FIG. 24, a third touch panel 98 may be included in thefourth apparatus 93 instead of the second touch panel 92.

The third touch panel 98 is substantially the same as the second touchpanel 92 except that the third touch panel 98 does not include thesecond layer structure 23 and the third electrodes 26 are disposed onthe first face 6 of the layer structure 5 in addition to the firstelectrodes 8. Each first electrode 8 is a continuous conductive regionextending in the first direction x in the same way as the second touchpanel 92, for example, each first electrode 8 may include several padsegments 94 evenly spaced in the first direction x and connected to oneanother in the first direction x by relatively narrow bridging segments95. Each third electrode 26 may comprise several pad segments 99 evenlyspaced in the second direction y in the same way as the second touchpanel 92. However, unlike the second touch panel 92, the pad segments 99of the third touch panel are disposed on the first face 6 of the layerstructure 5 and are interspersed with, and separated by, the firstelectrodes 8. The pad segments 99 corresponding to each third electrode26 are connected together by conductive jumpers 100. The jumpers 100each span a part of a first electrode 8 and the jumpers 10 o areinsulated from the first electrodes 8 by a thin layer of dielectricmaterial (not shown) which may be localised to the area around theintersection of the jumper 100 and the first electrode 8.

Alternatively, a dielectric layer (not shown) may overlie the first face6 of the layer structure 5 and the first and third electrode 8, 26.Conductive traces (not shown) extending in the second direction y may bedisposed over the dielectric layer (not shown), each conductive trace(not shown) overlying the pad segments 99 making up one third electrode26. The overlying conductive traces (not shown) may connect the padsegments 99 making up each third electrode 26 using vias (not shown)formed through the dielectric layer (not shown).

Fifth Combined Capacitance and Pressure Sensing Apparatus:

Referring also to FIG. 25, a fifth apparatus 93 including a second touchpanel 92, a second touch controller 102 and first and secondmultiplexers 75 a, 75 b will be explained.

The first multiplexer 75 a has a plurality of inputs and an outputcoupled to the terminal H. The second multiplexer 75 b has a pluralityof inputs and an output coupled to the terminal I.

The second touch panel 92 of the fifth apparatus 101 is the same as thesecond touch panel 92 of the fourth apparatus 93, except that each ofthe first electrodes 8 is coupled to a corresponding input of the firstmultiplexor 75 a by a respective first conductive trace 76 a, each ofthe third electrodes 26 is coupled to a corresponding input of thesecond multiplexer 75 b by a respective second conductive trace 76 b,and the second electrode 9 is coupled to a terminal J.

The second touch controller 102 includes the first and second front endmodules 3 a, 3 b, the second signal processing module 22 and thecontroller 79. Each of the first and second front end modules 3 a, 3 bis substantially the same as the front end module 3 of the third andfourth apparatuses 74, 93. The second signal processing module 22 issubstantially the same as the second signal processing module 22 of thesecond apparatus 20. The controller 79 is substantially the same as thecontroller 79 of the third or fourth apparatuses 74, 93, except that thecontrol signals 81 may cause the first and second multiplexers 75 a, 75b to address each given pair of first and third electrodes 8, 26according to a sequence determined by the controller 79 or communicatedto the controller 79 from the processor 32 by the link 800. The sequencemay be a predetermined sequence or a dynamically determined sequence.

In this way, each intersection of the first and third electrodes 8, 26effectively provides a second touch sensor 21 which may be individuallyaddressed by the first and second multiplexers 75 a, 75 b. When aparticular intersection is addressed by the first and secondmultiplexers 75 a, 75 b, a first input signal 11 a from the respectivefirst electrode 8 is received by the first front end module 3 a and asecond input signal 11 b from the respective third electrode 26 isconcurrently received by the second front end module.

Alternatively, the fifth apparatus 101 may use the third touch panel 98instead of the second touch panel 92.

In addition to changes in the self-capacitances of given first and thirdelectrode 8, 26 addressed by the multiplexers 75 a, 75 b, the respectivecapacitance values 19 a, 19 b also include a change in the mutualcapacitance between the addressed pair of first and third electrodes 8,26.

Referring also to FIG. 26, a configuration using first amplifier 50 toprovide the first stages 12 a, 12 b of the first and second front endmodules 3 a, 3 b will be explained.

A configuration of the fifth apparatus 101 including the first amplifier500 is substantially the same as the configuration of the third orfourth apparatuses 74, 93 including the first amplifier 50, except thata pair of multiplexers 75 a, 75 b, a pair of front end modules 3 a, 3 band a pair of first amplifiers 50 a, 50 b are used, and in that thefirst amplifiers 50 a, 50 b further include a first switch SW1 and asecond switch SW2.

The pair of first amplifiers 50 a, 50 b provide the first stages 12 a,12 b of the first and second front end modules 3 a, 3 b respectively.The first rail 53 of the first amplifier 50 a which is included in thefirst front end module 3 a is coupled via the terminal H to the outputof the first multiplexer 75 a. The first rail 53 of the first amplifier50 b which is included in the second front end module 3 b is coupled viathe terminal I to the output of the second multiplexer 75 b. The secondelectrode 9 of the second or third touch panels 92, 98 is coupled viaterminal J to the voltage bias source 52. The same voltage controlledsource V_(d)(f_(d)) may be coupled to both front end modules 3 a, 3 b inparallel.

The pair first amplifiers 50 a, 50 b include a first switch SW1 and asecond switch SW2. The first switch SW1 couples the first rail 53 to thesecond rail 55 of the first amplifier 50 s included in the first frontend module 3 a. The second switch SW2 couples the first rail 53 to thesecond rail 55 of the first amplifier 50 b included in the second frontend module 3 b. When the switch SW1 is closed, the first capacitor C_(f)of the first amplifier 50 a is discharged. When the switch SW2 isclosed, the first capacitor C_(f) of the first amplifier 50 b isdischarged. The opening and closing of the switches SW1, SW2 may begoverned by control signals 82 provided by the controller 79. In thisway, after the first front end module 3 a has received an input signal11 from one of the first electrodes 8 and the second front end module 3b has received an input signal 11 from one of the third electrodes 26,the capacitors C_(f) of the first amplifiers 50 a, 50 b may bedischarged so as to reset the respective feedback networks before themultiplexers 75 a, 75 b connect a different pairing of first and thirdelectrodes 8, 26.

Thus, each first amplifier 50 a, 50 b provides a corresponding amplifiedsignal 15 a, 15 b depending upon first and second input signals 11 a, 11b received from the first and third electrodes 8, 26 addressed by therespective first and second multiplexers 75 a, 75 b. One difference tothe third or fourth apparatuses 74, 93 is that the equivalent circuit 56of each second touch sensor 21 provided by an addressed pair of firstand second electrodes 8, 26 additionally includes a mutual capacitanceC_(mut) between the selected first electrode 8 and the selected thirdelectrode 26.

Alternatively, the fifth apparatus 102 may be configured using first andsecond front end modules 3 a, 3 b including respective second amplifiers57. In such a case, the first rail 58 of the second amplifier 57included in the first front end module 3 a may be coupled to the outputof the first multiplexer 75 a via the terminal H, the first rail 58 ofthe second amplifier 57 included in the second front end module 3 b maybe coupled to the output of the second multiplexer 75 b via the terminalI, and the second electrode 9 of the second or third touch panels 92, 98may be coupled via terminal J to a voltage bias source 52.

Alternatively, the fifth apparatus 102 may be configured using first andsecond front end modules 3 a, 3 b including respective third amplifiers63. In such a case, the first rail 64 of the third amplifier 63 includedin the first front end module 3 a may be coupled to the terminal H andthe corresponding second rail 66 may be coupled to the terminal J, andthe first rail 64 of the third amplifier 63 included in the second frontend module 3 b may be coupled to the terminal I and the correspondingsecond rail 66 may be coupled to the terminal J. Alternatively, thefirst rail 64 of the third amplifier 63 included in the first front endmodule 3 a may be coupled to the terminal J and the corresponding secondrail 66 may be coupled to the terminal H, and the first rail 64 of thethird amplifier 63 included in the second front end module 3 b may becoupled to the terminal J and the corresponding second rail 66 may becoupled to the terminal I.

Alternatively, the fifth apparatus 102 may be configured using first andsecond front end modules 3 a, 3 b including respective fourth amplifiers67. In such a case, the first rail 68 of the fourth amplifier 67included in the first front end module 3 a may be coupled to theterminal H and the corresponding second rail 70 may be coupled to theterminal J, and the first rail 68 of the fourth amplifier 67 included inthe second front end module 3 b may be coupled to the terminal I and thecorresponding second rail 70 may be coupled to the terminal J.Alternatively, the first rail 68 of the fourth amplifier 67 included inthe first front end module 3 a may be coupled to the terminal J and thecorresponding second rail 70 may be coupled to the terminal H, and thefirst rail 68 of the fourth amplifier 67 included in the second frontend module 3 b may be coupled to the terminal J and the correspondingsecond rail 70 may be coupled to the terminal I

Sixth Combined Capacitance and Pressure Sensing Apparatus and FourthTouch Panel:

Referring also to FIGS. 27 and 28, a sixth apparatus 104 including afourth touch panel 103, a third touch controller 105 and first andsecond multiplexers 75 a, 75 b will be explained.

The sixth apparatus 104 includes first and second multiplexers 75 a, 75b, a fourth touch panel 103 and a third touch controller 105. In manyrespects the sixth apparatus 104 is substantially similar or analogousto the third to fifth apparatuses 74, 93, 101, and only the differencesof the sixth apparatus 104 shall be explained.

The first and second multiplexers 75 a, 75 b each include a plurality ofinputs and an output. The output of the first multiplexer 75 a iscoupled to a terminal K and the output of the second multiplexer 75 b iscoupled to a terminal L.

The fourth touch panel 103 includes a layer structure 5 which isgenerally the same as the layer structure 5 of the first touch sensor 1,except that in the fourth touch panel 103, the layer structure 5 iscommon to many first electrodes 8 disposed on the first face 6 of thelayer structure 5 and many second electrodes 9 disposed on the secondface 7 of the layer structure 5. The first electrodes 8 each extend inthe first direction x and the first electrodes 8 are disposed in anarray evenly spaced in the second direction y. The second electrodes 9each extend in the second direction y and the second electrodes 9 aredisposed in an array evenly spaced in the first direction x. Each secondelectrode 9 is coupled to a corresponding input of the first multiplexer75 a by a respective conductive trace 76 a, and each first electrode 8is coupled to a corresponding input of the second multiplexer 75 b by arespective conductive trace 76 b. In this way, the area around eachintersection of a first electrode 8 with a second electrode 9effectively provides a first touch sensor 2 and each of the first andsecond 8, 9 electrodes may be individually addressed using the first andsecond multiplexers 75 a, 75 b and the conductive traces 76 a, 76 b.

The fourth touch panel 103 may be bonded overlying the display 37 of anelectronic device 28 and a cover lens 77 may be bonded overlying thefourth touch panel 103 in the same way as for the touch panel 29, thesecond touch panel 92 or the third touch panel 98.

The third touch controller 105 includes a front end module 3, a signalsource 44, a signal processing module 4 and a controller 79 which arethe same as hereinbefore described, except that the first stage 12 ofthe front end module 3 uses the third amplifier 63 of the fourthamplifier 67 and the signal source 44 is one or more synchronisedcurrent controlled sources I_(d)(f_(d)). In this case, the front endmodule 3 is connected across the terminals K and L.

The controller 79 may provide a control signal 81 to the first andsecond multiplexers 75 a, 75 b in the same way as for the fifthapparatus 110. In this way, each intersection of the first and thirdelectrodes 8, 26 effectively provides a first touch sensor 2 which maybe individually addressed by the first and second multiplexers 75 a, 75b.

In addition to changes in the self-capacitances of given first andsecond electrodes 8, 9 addressed by the multiplexers 75 a, 75 b, thecapacitance values 19 also include a change in the mutual capacitancebetween the addressed pair of first and second electrodes 8, 9.

Although the first electrode 8 and the third electrode 26 have beenshown as being substantially rectangular, other shapes can be used. Forexample, the first and second electrodes 8, 9 of the fourth touch panel103 may have shapes and configurations substantially similar to thefirst and third electrodes 8, 26 of the second touch panel 92.

Referring also to FIG. 29, a configuration of the third amplifier 63included in the sixth apparatus 104 will be explained.

The first rail 64 of the third amplifier 63 may be coupled to theterminal K and the second rail 66 may be coupled to the terminal L.Alternatively, first rail 64 of the third amplifier 63 may be coupled tothe terminal L and the second rail 66 may be coupled to the terminal K.

Alternatively, the fourth amplifier 67 may be included in the sixthapparatus 104. In such a case, the first rail 68 of the fourth amplifier67 may be coupled to the terminal K and the second rail 70 may becoupled to the terminal L. Alternatively, first rail 68 of the fourthamplifier 67 may be coupled to the terminal L and the second rail 700may be coupled to the terminal K.

First Display Stack Up:

Referring also to FIGS. 30A to 30C, a first display stack-up 1006 and amethod of fabricating the first display stack 106 up will be explained.

Referring in particular to FIG. 30A, the cover lens 77 is a transparentsubstrate extending in the first x and second y directions and havingfirst 77 a and second 77 b opposite faces. A first dielectric layer 107extends in the first x and second y directions and has first 107 a andsecond 107 b opposite faces. Third electrodes 26 in the form of a set ofconductive regions extending in the first direction x and spaced apartin the second direction y are disposed on the second face 107 b of thefirst dielectric layer 107. The second face 107 b of the firstdielectric layer 107 is bonded to the first face 77 a of the cover lens77.

Referring in particular to FIG. 30B, a second dielectric layer 108extends in the first x and second y directions and has first 108 a andsecond 108 b opposite faces. First electrodes 8 in the form of a set ofconductive regions extending in the second direction y and spaced apartin the first direction x are disposed on the second face 108 b of thesecond dielectric layer 108. The second face 108 b of the seconddielectric layer 108 is bonded to the first face 107 a of the firstdielectric layer 107.

Referring in particular to FIG. 30C, a layer of piezoelectric material10 extends in the first x and second y directions and has first 10 a andsecond 10 b opposite faces. A second electrode 9 in the form of aconductive material region is disposed on the first face 10 a of thelayer of piezoelectric material 10 such that, when assembled, the secondelectrode 9 at least partially overlaps each first electrode 8 and eachthird electrode 26 region. The second face 10 b of the layer ofpiezoelectric material to is bonded to the first face 108 a of thesecond dielectric layer 108.

The first display stack-up 106 may be bonded overlying the display 37 ofan electronic device 28. The elements of the first display stack-up 106are stacked in the thickness direction z from the display 37 to thecover lens 77. The layer structure 5 includes the second dielectriclayer 108 and the layer of piezoelectric material 10 and the secondlayer structure 23 includes the first dielectric layer 108.

The cover lens 77 is made of glass, or PET or any other substantiallytransparent material. The cover lens 7 may be up to about 20 mm thickand may be at least 0.05 mm thick. Preferably, the cover lens 77 is upto about 2 mm thick and may be at least 0.05 mm thick. The layer ofpiezoelectric material 10 is made of PVDF or any other substantiallytransparent piezoelectric material. The layer of piezoelectric materialto may be poled before assembling the first stack-up 1006.Alternatively, the layer of piezoelectric material may be poled afterassembling the first stack-up 106. The layer of piezoelectric materialmay be up to about 10 μm thick, and may be at least 0.5 μm or at least 1μm thick. The second electrode 9 and the first electrodes 8 and/or thirdelectrodes 26 may be used to produce a poling field. The dielectriclayers 107, 108 may be PET or any other substantially transparentpolymer. The dielectric layers 107, 108 may be between 10 μm and 100 μmthick, for example, around 20 to 25 μm thick. Preferably the dielectriclayers 107, 108 are in the range of about 10-100 μm thick. Theconductive regions providing the electrodes 8, 9, 26 may be ITO, IZO orany other substantially transparent conductive material. The conductiveregions providing the electrodes 8, 9, 26 may be applied to thedielectric layers 107, 108 and/or the layer of piezoelectric material 10using lithography, printing or other suitable methods. The shapes of theconductive regions providing the first, second and third electrodes 8, 926 may be any suitable electrode shape described in relation to one ofthe third to sixth apparatuses 74, 93, 101, 104. The sheet resistance ofconductive regions providing electrodes may be between 1 and 200 Ω/sq.The sheet resistance may be below 10 Ω/sq. Preferably the sheetresistance is as low as is practical.

The assembly of the first display stack-up 106 has been described in acertain sequence. However, the elements of the first display stack-upmay be bonded together in any other sequence resulting in the sameordering of layers 107, 108, 10. In particular, the first and seconddielectric layers 107, 108 and the layer of piezoelectric material tomay be bonded together using continuous roll-to-roll production methodsbefore being bonded to the cover lens 77. When the cover lens 77 is aflexible material, the first display stack-up 1006 may be fabricatedentirely using continuous roll-to-roll processes.

The first display stack-up 106 does not require complex patterning ofthe layer of piezoelectric material to or of electrodes disposed on thelayer of piezoelectric material 10. This allows fabrication of the firstdisplay stack-up to avoid complex multi-stage and/or duplex patterningof electrodes. As a result, fabrication of the first display stack-up106 may be fast, efficient and cheap.

Second Display Stack-Up:

Referring also to FIGS. 31A to 31C, a second display stack-up 109 and amethod of fabricating the second display stack-up log will be explained.

The second display stack-up 109 is the same as the first displaystack-up 106, except that elements of the second display stack-up 109are bonded to one another using layers of pressure sensitive adhesive(PSA) material 110 extending in the first x and second y directions. Forexample, the cover lens 77 and the first dielectric layer 117 arearranged so that the first face 77 a of the cover lens 77 is opposite toand separated from the second face 107 b of the first dielectric layer107. Pressure applied in the thickness direction z to bond the coverlens 77 and the first dielectric layer 107 together. Layers of PSAmaterial 110 are used in the same way to bond the first and seconddielectric layers 107, 108, to bond the second dielectric layer 108 tothe layer of piezoelectric material to and to bond the second stack-up109 overlying the display 37. Layers of PSA material 100 may be between10 and 50 μm thick. Preferably, the layers of PSA material 110 are 25 μmthick.

The elements of the second display stack-up 109 are stacked in thethickness direction z from the display 37 to the cover lens 77. Thelayer structure 5 includes the second dielectric layer 108, the layer ofpiezoelectric material 10 and a layer of PSA material 110. The secondlayer structure 23 includes the first dielectric layer 107 and a layerof PSA material 110 .

Third Display Stack-Up:

Referring also to FIGS. 32A to 32C, a third display stack-up 111 and amethod of fabricating the third display stack-up 111 will be explained.

Referring in particular to FIG. 32A, the cover lens 77 is a transparentsubstrate extending in the first x and second y directions and havingfirst 77 a and second 77 b opposite faces. A first dielectric layer 107extends in the first x and second y directions and has first 107 a andsecond 107 b opposite faces. Third electrodes 26 in the form of a set ofconductive regions extending in the first direction x and spaced apartin the second direction y are disposed on the second face 107 b of thefirst dielectric layer 107. The second face 107 b of the firstdielectric layer 107 is bonded to the first face 77 a of the cover lens77 using a layer of PSA material 110.

Referring in particular to FIG. 32B, a layer of piezoelectric materialto extends in the first x and second y directions and has first 10 a andsecond 10 b opposite faces. First electrodes 8 in the form of conductiveregions extending in a second direction y and spaced apart in the firstdirection x are disposed on the second face 10 b of the layer ofpiezoelectric material 10. A second electrode 9 in the form of aconductive material region is disposed on the first face 10 a of thelayer of piezoelectric material 10 such that, when assembled, the secondelectrode 9 at least partially overlaps each first electrode 8 and eachthird electrode 26. The second face 10 b of the layer of piezoelectricmaterial to may be bonded to the first face 107 a of the firstdielectric layer 107 using a layer of PSA material 110 .

Referring in particular to FIG. 32C, the third display stack up 111 maybe bonded overlying the display 37 using a layer of PSA material 100 .

The elements of the third display stack-up 1 n are stacked in thethickness direction z from the display 37 to the cover lens 77. Thelayer structure 5 includes the layer of piezoelectric material to. Thesecond layer structure 23 includes the first dielectric layer 107 and alayer of PSA material 110.

Fourth Display Stack-Up:

Referring also to FIGS. 33A to 33D, a fourth display stack-up 112 and amethod of fabricating the fourth display stack-up 112 will be explained.

Referring in particular to FIG. 33A, the cover lens 77 is a transparentsubstrate extending in the first x and second y directions and havingfirst 77 a and second 77 b opposite faces. A first dielectric layer 107extends in the first x and second y directions and has first 107 a andsecond 107 b opposite faces. Third electrodes 26 in the form of a set ofconductive regions extending in the first direction x and spaced apartin the second direction y are disposed on the second face 107 b of thefirst dielectric layer 107. The second face 107 b of the firstdielectric layer 107 is bonded to the first face 77 a of the cover lens7 using a layer of PSA material 110 .

Referring in particular to FIG. 33B, a second dielectric layer 108extends in the first x and second y directions and has first 108 a andsecond 108 b opposite faces. First electrodes 8 in the form of a set ofconductive regions extending in the second direction y and spaced apartin the first direction x are disposed on the second face 108 b of thesecond dielectric layer 108. The second face 108 b of the seconddielectric layer 108 is bonded to the first face 107 a of the firstdielectric layer 107 using a layer of PSA material 110.

Referring in particular to FIG. 33C, a layer of piezoelectric materialto extends in the first x and second y directions and has first 10 a andsecond 10 b opposite faces. The second face 10 b of the layer ofpiezoelectric material to is bonded to the first face 108 a of thesecond dielectric layer 108 using a layer of PSA material 110.

Referring in particular to FIG. 33D, a third dielectric layer 113extends in the first x and second y directions and has first 113 a andsecond 113 b opposite faces. A second electrode 9 in the form of aconductive material region is disposed on the second face 113 b of thelayer third dielectric layer 113 such that, when assembled, the secondelectrode 9 at least partially overlaps each first electrode 8 and eachthird electrode 26 region. The third dielectric layer 113 issubstantially the same as the first or second dielectric layers 107,108. The second face 13 b of third dielectric layer 113 is bonded to thefirst face 10 a of the layer of piezoelectric material to using a layerof PSA material 110.

The fourth display stack-up 112 may be bonded overlying the display 37of an electronic device 28. The elements of the fourth display stack-up112 are stacked in the thickness direction z from the display 37 to thecover lens 77. The layer structure 5 includes the second dielectriclayer 108, the layer of piezoelectric material to and two layers of PSAmaterial 110. The second layer structure 23 includes the firstdielectric layer 107 and a layer of piezoelectric material 110.

Thus, in the fourth display stack-up, the layer of piezoelectricmaterial 10 does not have any electrodes disposed thereon. Thissimplifies the fabrication of the fourth stack-up substantially becauseprocessing steps to deposit electrodes on the layer of piezoelectricmaterial 10 are not required. In a case when the layer of piezoelectricmaterial to is PVDF, the fourth stack-up 112 can be fabricated bysandwiching a PVDF film providing the layer of piezoelectric material 10between PET layers bearing patterned and unpatterned ITO electrodes. Inthis way, methods for manufacturing a regular projected capacitancetouch panel may be quickly and easily adapted to allow production ofcombined pressure and capacitance touch panels.

Fifth Display Stack-Up:

Referring also to FIGS. 34A and 34B, a fifth display stack-up 114 and amethod of fabricating the fifth display stack-up 114 will be explained.

Referring in particular to FIG. 34A, the cover lens 77 is a transparentsubstrate extending in the first x and second y directions and havingfirst 77 a and second 77 b opposite faces. A fourth dielectric layer 115extends in the first x and second y directions and has first 115 a andsecond 115 b opposite faces. Third electrodes 26 in the form of a set ofconductive regions extending in the first direction x and spaced apartin the second direction y are disposed on the second face 115 b of thefourth dielectric layer 115. First electrodes 8 in the form of a set ofconductive regions extending in the second direction y and spaced apartin the first direction x are disposed on the first face 15 a of thefourth dielectric layer 115. The second face 115 b of the fourthdielectric layer 115 is bonded to the first face 77 a of the cover lens77 using a layer of PSA material 110. The fourth dielectric layer 115 issubstantially the same as the first, second or third dielectric layers107, 108, 113.

Referring in particular to FIG. 34B, a layer of piezoelectric material10 extends in the first x and second y directions and has first 10 a andsecond 10 b opposite faces. A second electrode 9 in the form of aconductive material region is disposed on the first face 10 a of thelayer of piezoelectric material 10 such that, when assembled, the secondelectrode 9 at least partially overlaps each first electrode 8 and eachthird electrode 26 region. The second face 10 b of the layer ofpiezoelectric material 10 is bonded to the first face 115 a of thefourth dielectric layer 115 using a layer of PSA material 110.

The fifth display stack-up 114 may be bonded overlying the display 37 ofan electronic device 28 using a layer of PSA material 110. The elementsof the fifth display stack-up 114 are stacked in the thickness directionz from the display 37 to the cover lens 77. The layer structure 5includes the layer of piezoelectric material 10 and a layer of PSAmaterial 110. The second layer structure 23 includes the fourthdielectric layer 115.

The second electrode 9 need not be disposed on the layer ofpiezoelectric material 10. Alternatively, the fifth display stack-up 114may include the third dielectric layer 113 with the second face 113 b ofthe third dielectric layer 113 bonded to the first face 10 a of thelayer of piezoelectric material 10 using a layer of PSA material 110 .

Sixth Display Stack-Up:

Referring also to FIGS. 35A and 35B, a sixth display stack-up 116 and amethod of fabricating the sixth display stack-up 116 will be explained.

Referring in particular to FIG. 35A, the cover lens 77 is a transparentsubstrate extending in the first x and second y directions and havingfirst 77 a and second 77 b opposite faces. A fifth dielectric layer 117extends in the first x and second y directions and has first 117 a andsecond 117 b opposite faces. Third electrodes 26 in the form of a set ofconductive regions extending in the first direction x and spaced apartin the second direction y are disposed on the second face 117 b of thefifth dielectric layer 117. First electrodes 8 in the form of a set ofconductive regions extending in the second direction y and spaced apartin the first direction x are disposed on the second face 117 a of thefifth dielectric layer 117. The second face 117 b of the fifthdielectric layer 117 is bonded to the first face 7 a of the cover lens77 using a layer of PSA material 110. The fifth dielectric layer 115 issubstantially the same as the first, second, third of fourth dielectriclayers 107, 108, 113, 115. Each first electrode 8 is a continuousconductive region and each third electrode is made up of a number ofseparate conductive regions connected by jumpers 100. Each jumper spansa portion of a conductive region belonging to a first electrode 8. Thefirst and third electrodes 8, 26 may be substantially the same as thefirst and third electrodes 8, 26 of the third touch panel 98.

Referring in particular to FIG. 34B, a layer of piezoelectric material10 extends in the first x and second y directions and has first 10 a andsecond 10 b opposite faces. A second electrode 9 in the form of aconductive material region is disposed on the first face 10 a of thelayer of piezoelectric material 10 such that, when assembled, the secondelectrode 9 at least partially overlaps each first electrode 8 and eachthird electrode 26 region. The second face 10 b of the layer ofpiezoelectric material to is bonded to the first face 117 a of the fifthdielectric layer 117 using a layer of PSA material 110.

The sixth display stack-up 116 may be bonded overlying the display 37 ofan electronic device 28 using a layer of PSA material 110. The elementsof the sixth display stack-up 116 are stacked in the thickness directionz from the display 37 to the cover lens 77. The layer structure 5includes the layer of piezoelectric material 10, a layer of PSA material110 and the fifth dielectric layer 17.

The second electrode 9 need not be disposed on the layer ofpiezoelectric material 10. Alternatively, the sixth display stack-up 116may include the third dielectric layer 113 with the second face 113 b ofthe third dielectric layer 113 bonded to the first face 10 a of thelayer of piezoelectric material to using a layer of PSA material 110.

Seventh Display Stack-Up:

Referring also to FIGS. 36A to 36C, a seventh display stack-up 118 and amethod of fabricating the seventh display stack-up 118 will beexplained.

Referring in particular to FIG. 36A, the cover lens 77 is a transparentsubstrate extending in the first x and second y directions and havingfirst 7 a and second 77 b opposite faces. Third electrodes 26 in theform of a set of conductive regions extending in the first direction xand spaced apart in the second direction y are disposed on the firstface 77 a of the cover lens 77.

Referring in particular to FIG. 36B, a second dielectric layer 108extends in the first x and second y directions and has first 108 a andsecond 108 b opposite faces. First electrodes 8 in the form of a set ofconductive regions extending in the second direction y and spaced apartin the first direction x are disposed on the second face 108 b of thesecond dielectric layer 108. The second face 108 b of the seconddielectric layer 108 is bonded to the first face 77 a of the cover lens77 using a layer of PSA material 110.

Referring in particular to FIG. 36C, a layer of piezoelectric material10 extends in the first x and second y directions and has first 10 a andsecond 10 b opposite faces. A second electrode 9 in the form of aconductive material region is disposed on the first face 10 a of thelayer of piezoelectric material to such that, when assembled, the secondelectrode 9 at least partially overlaps each first electrode 8 and eachthird electrode 26 region. The second face 10 b of the layer ofpiezoelectric material 10 is bonded to the first face 108 a of thesecond dielectric layer 108 using a layer of PSA material 110 .

The seventh display stack-up 118 may be bonded overlying the display 37of an electronic device 28 using a layer of PSA material 110. Theelements of the seventh display stack-up 118 are stacked in thethickness direction z from the display 37 to the cover lens 7. The layerstructure 5 includes the layer of piezoelectric material 10, a layer ofPSA material 110 and the second dielectric layer 108. The second layerstructure 23 includes a layer of PSA material 110 .

The second electrode 9 need not be disposed on the layer ofpiezoelectric material 10. Alternatively, the seventh display stack-up118 may include the third dielectric layer 113 with the second face 113b of the third dielectric layer 113 bonded to the first face 10 a of thelayer of piezoelectric material to using a layer of PSA material 110.

Eighth Display Stack-Up:

Referring also to FIGS. 37A to 37D, an eighth display stack-up 125 and amethod of fabricating the eighth display stack-up 125 will be explained.

Referring in particular to FIG. 37A, the cover lens 77 is a transparentsubstrate extending in the first x and second y directions and havingfirst 77 a and second 77 b opposite faces. First electrodes 8 in theform of a set of conductive regions extending in the second direction yand spaced apart in the first direction x are disposed on the first face77 a of the cover lens 77. Third electrodes 26 in the form of a set ofconductive regions extending in the first direction x and spaced apartin the second direction y are also disposed on the first face 77 a ofthe cover lens 77. Each first electrode 8 is a continuous conductiveregion and each third electrode is made up of a number of separateconductive regions connected by jumpers 100. Each jumper spans a portionof a conductive region belonging to a first electrode 8. The first andthird electrodes 8, 26 may be substantially similar to the first andthird electrodes 8, 26 of the third touch panel 98.

Referring in particular to FIG. 37B, a layer of piezoelectric materialto extends in the first x and second y directions and has first 10 a andsecond 10 b opposite faces. The second face 10 b of the layer ofpiezoelectric material to is bonded to the first face 77 a of the coverlens 77 using a layer of PSA material 110 .

Referring in particular to FIG. 37C, a third dielectric layer 113extends in the first x and second y directions and has first 1 i 3 a andsecond 113 b opposite faces. A second electrode 9 in the form of aconductive material region is disposed on the second face 113 b of thethird dielectric layer 113 such that, when assembled, the secondelectrode 9 at least partially overlaps each first electrode 8 and eachthird electrode 26 region. The second face 113 b of third dielectriclayer 113 is bonded to the first face 10 a of the layer of piezoelectricmaterial to using a layer of PSA material 110.

Referring in particular to FIG. 37D, the eighth display stack-up 125 maybe bonded overlying the display 37 of an electronic device 28 using alayer of PSA material 110 to bond the first surface 113 a of the thirddielectric layer 113 to the display 37. The elements of the eighthdisplay stack-up 125 are stacked in the thickness direction z from thedisplay 37 to the cover lens 7. The layer structure 5 includes the layerof piezoelectric material to and two layers of PSA material 110.

The second electrode 9 need not be disposed on the third dielectriclayer 113. Alternatively, the eighth display stack-up 125 may include alayer of piezoelectric material to having the second electrode 9disposed onto the first face 10 a of the layer of piezoelectric material10 .

Modifications

It will be appreciated that many modifications may be made to theembodiments hereinbefore described. Such modifications may involveequivalent and other features which are already known in the design,manufacture and use of projected capacitance touch panels and which maybe used instead of or in addition to features already described herein.Features of one embodiment may be replaced or supplemented by featuresof another embodiment.

For example, touch panels 29, 92, 98, 103 and stack-ups 106, 109, 111,112, 114, 116, 118, 125 have been described which overlie the display 37of an electronic device 28. However, the apparatuses 1, 20, 74, 93,1010, 104 described herein may equally be used with other touch panelswhich are integrated into a display 37 such as, for example, an LCDdisplay, an OLED display, a plasma display or an electrophoreticdisplay.

Referring also to FIG. 38, a first embedded stack-up 119 includes apixel array 120 of a display 37, a colour filter glass 121, first andthird electrodes 8, 26, a layer structure 5, a patterned secondelectrode 83, a polariser 122 and a cover lens 77 stacked in thethickness direction from the pixel array 120 to the cover lens 77. Thefirst and third electrodes 8, 26 are disposed on the same face of thelayer structure 5 in substantially the same way as the third touch panel98.

In this way, the first embedded stack-up 119 can be used in the fourthof fifth apparatuses 93, lot to provide a touch panel with combinedcapacitive and pressure sensing embedded within an LCD display. This mayallow the total thickness of the display 37 and touch panel to bereduced compared to a touch panel overlying the display 37.

Referring also to FIG. 39, a second embedded stack-up 123 includes apixel array 120 of a display 37, third electrodes 26, a colour filterglass 121, first electrodes 8, a layer structure 5, a patterned secondelectrode 83, a polariser 122 and a cover lens 77 stacked in thethickness direction from the pixel array 120 to the cover lens 77. Thefirst and third electrodes 8, 26 are disposed 5 in substantially thesame way as the second touch panel 92, except that the first and thirdelectrodes 8, 26 are disposed on opposite sides of the colour filterglass 121 instead of the second layer structure 23.

Referring also to FIG. 40, a third embedded stack-up 124 includes apixel array 120 of a display 37, third electrodes 26, a second layerstructure 23, first electrodes 8, a colour filter glass 121, a layerstructure 5, a patterned second electrode 83, a polariser 122 and acover lens 77 stacked in the thickness direction from the pixel array120 to the cover lens 77. The first and third electrodes 8, 26 aredisposed in substantially the same way as the second touch panel 92.

In the third embedded stack-up 124, the first and third electrodes 8, 26are separated by the second layer structure 23. However, the thirdembedded stack-up 124 may alternatively omit the second layer structureand include first and third electrodes 8, 26 disposed in substantiallythe same way as the third touch panel 98.

Referring also to FIG. 41, a fourth embedded stack-up 126 includes apixel array 120 of a display 37, a colour filter glass 121, first andthird electrodes 8, 26, a polariser 122, a layer structure 5, apatterned second electrode 83, and a cover lens 7 stacked in thethickness direction from the pixel array 120 to the cover lens 77. Thefirst and third electrodes 8, 26 are disposed on the same face of thelayer structure 5 in substantially the same way as the third touch panel98.

Referring also to FIG. 42, a fifth embedded stack-up 127 includes apixel array 120 of a display 37, third electrodes 26, a colour filterglass 121, first electrodes 8, a polariser 122, a layer structure 5, apatterned second electrode 83, and a cover lens 77 stacked in thethickness direction from the pixel array 120 to the cover lens 77. Thefirst and third electrodes 8, 26 are disposed 5 in substantially thesame way as the second touch panel 92, except that the first and thirdelectrodes 8, 26 are disposed on opposite sides of the colour filterglass 121 instead of the second layer structure 23.

Referring also to FIG. 43, a sixth embedded stack-up 128 includes apixel array 120 of a display 37, third electrodes 26, a second layerstructure 23, first electrodes 8, a layer structure 5, a colour filterglass 121, a patterned second electrode 83, a polariser 122 and a coverlens 7 stacked in the thickness direction from the pixel array 120 tothe cover lens 77. The first and third electrodes 6, 26 are disposed insubstantially the same way as the second touch panel 92.

Referring also to FIG. 44, a seventh embedded stack-up 129 includes apixel array 120 of a display 37, third electrodes 26, a second layerstructure 23, first electrodes 8, a layer structure 5, a patternedsecond electrode 83, a colour filter glass 121, a polariser 122 and acover lens 77 stacked in the thickness direction from the pixel array120 to the cover lens 77. The first and third electrodes 8, 26 aredisposed in substantially the same way as the second touch panel 92.

Referring also to FIG. 45, an eighth embedded stack-up 130 includes apixel array 120 of a display 37, third electrodes 26, a second layerstructure 23, first electrodes 8, a colour filter glass 121, a polariser122, a layer structure 5, a patterned second electrode 83 and a coverlens 77 stacked in the thickness direction from the pixel array 120 tothe cover lens 77. The first and third electrodes 8, 26 are disposed insubstantially the same way as the second touch panel 92.

The sixth, seventh and eighth embedded stack-ups 128, 129, 130 have beendescribed with the first and third electrodes 8, 26 separated by thesecond layer structure 23. However, the sixth, seventh and eighthembedded stack-ups 128, 129, 130 may alternatively omit the second layerstructure and include first and third electrodes 8, 26 disposed insubstantially the same way as the third touch panel 98.

The first to eighth embedded stack-ups, 119, 123, 124, 126, 127, 128,129, 130 have been described as including the patterned second electrode83. However, the patterned second electrode 83 need not be used and thefirst to eighth embedded stack-ups, 119, 123, 124, 126, 127, 128, 129,130 may instead include un-patterned second electrodes 9.

Touch panels have been described in which first and third electrodes 8,26 are separated from second, or bias, electrodes 9, 83 by the layerstructure 5. However, other arrangements are possible. Referring toFIGS. 46 and 47, a fifth touch panel 131 includes a layer structure 5, aplurality of first electrodes 8 disposed on the first face 6 of thelayer structure 5, a plurality of third electrodes 26 disposed on thesecond face 7 of the layer structure 5 and a plurality of secondelectrodes 9 disposed on the second face 7 of the layer structure 5 inthe form of a plurality of separated second electrodes 132.

The first electrodes 8 extend in the first direction x and are spacedapart in the second direction y. The third electrodes 26 extend in thesecond direction y and are spaced apart in the first direction x. Theseparated second electrodes 132 extend in the second direction y arespaced apart in the first direction x. The separated second electrodes132 and the third electrodes 26 are interleaved and do not contact oneanother. The separated second electrodes 132 and third electrodes 26 maybe read using conductive traces (not shown) which exit the fifth touchpanel 131 on different edges. Each first electrode 8 may take the formof several pad segments 94 evenly spaced in the first direction x andconnected to one another in the first direction x by relatively narrowbridging segments 95. Similarly, each third electrode 26 may includeseveral pad segments 96 evenly spaced in the second direction y andconnected to one another in the second direction y by relatively narrowbridging segments 97. The pad segments 94 of the first electrodes 8 maybe diamond shaped. The pad segments 96 and bridging segments 97 of thethird electrodes 26 may have the same respective shapes and widths asthe first electrodes 8. Each separated second electrode 9 may includeseveral pad segments 133 evenly spaced in the second direction y andconnected to one another in the second direction y by relatively narrowbridging segments 134. The pad segments 133 and bridging segments 134 ofthe separated second electrodes 132 may have the same respective shapesand widths as the first and third electrodes 8, 26. Alternatively, thepad segments 94 of the first electrodes 8 may be larger or smaller thanthe pad segments 133 of the separated second electrodes 132.

The first electrodes 8 and the third electrodes 26 are arranged suchthat the bridging segments 97 of the third electrodes 26 overlie thebridging segments 95 of the first electrodes 8. The first electrodes 8and the third electrodes 26 are arranged such that the respective padsegments 94, 96 do not overlap. Instead, the separated second electrodesare arranged such that the pad segments 133 of the separated secondelectrodes 132 overlap the pad segments 94 of the first electrodes 8.The pad segments 94, 96, 133 need not be diamond shaped, and may insteadbe circular. The pad segments 94, 96, 133 may be a regular polygon suchas a triangle, square, pentagon or hexagon.

The fifth touch panel may be used in, for example, the fourth of fifthapparatus 93, 101 to measure mutual capacitance between a pair of firstand third electrodes 8, 26. The separated sensing electrodes 132 may becoupled to each another, for example using external traces (not shown)and addressed collectively to measure pressure values between a firstelectrode 8 and the separated sensing electrodes 132. Alternatively, theseparated sensing electrodes 132 may be individually addressable tomeasure pressure values using a pair of first and separated secondelectrodes 8, 132.

The first to eighth display stack ups 06, 109, 111, 112, 114, 116, 118,125 or the first to eighth embedded stack-ups, 119, 123, 124, 126, 127,128, 129, 130 may be adapted to incorporate the fifth touch panel 131,or elements of the fifth touch panel 131 such as, for example, disposingthe third electrodes 26 on the same surface as the separated secondelectrode 132. The separated second electrodes 132 need not be disposedon the same surface as the third electrode 26, and may alternatively bedisposed on the same surface of the layer structure 5 as the firstelectrodes 8.

Touch panels and stack-ups have been described which are generallyplanar. However, touch panels and stack-ups need not be planar or flatand may provide curved or other non-planar surfaces for a user tointeract with. Touch panels and stack-ups may be provided overlying orembedded within curved displays.

The signal processing module 4, 22, controller 79 or processer 32 mayemploy correlated double sampling methods to improve the signal to noiseratio of the pressure values 18 and/or the capacitance values 19. Thesignal processing module 4, 22, controller 79 or processer 32 mayprocess the pressure values 18 and/or the capacitance values 19 as imagedata.

Touch sensors 2, 21 and touch panels 29, 92, 98, 103 have been generallydescribed in relation to first, second and third directions x, y, zforming an orthogonal set. However, the first and second directions neednot be perpendicular and may in general intersect at any angle between 1degree and 90 degrees. Intersection of the first and second directionsat 90, 60, 45 or 30 degrees is preferred.

Although claims have been formulated in this application to particularcombinations of features, it should be understood that the scope of thedisclosure of the present invention also includes any novel features orany novel combination of features disclosed herein either explicitly orimplicitly or any generalization thereof, whether or not it relates tothe same invention as presently claimed in any claim and whether or notit mitigates any or all of the same technical problems as does thepresent invention. The applicant hereby gives notice that new claims maybe formulated to such features and/or combinations of such featuresduring the prosecution of the present application or of any furtherapplication derived therefrom.

What is claimed is:
 1. A device for processing signals from a touchpanel, the touch panel comprising a layer of piezoelectric materialdisposed between a plurality of first electrodes and at least one secondelectrode, each first electrode having a location, the device configuredto: receive signals from the first electrodes; generate pressure signalsindicative of pressures applied to the touch panel proximate tocorresponding first electrodes; and, estimate one or more userinteraction locations based on interpolation of the pressure signals andthe locations of the corresponding first electrodes.
 2. A deviceaccording to claim 1, wherein each user interaction location isestimated based on a locally maximum pressure signal corresponding to aclosest first electrode, and on pressure signals corresponding to one ormore first electrodes proximate to the closest first electrode.
 3. Adevice according to claim 1, wherein each user interaction location isestimated based on a locally maximum pressure signal corresponding to aclosest first electrode, and on two next largest pressure signal valuescorresponding to first electrodes adjacent to the closest electrode. 4.A device according to claim 1, wherein each user interaction location isestimated based on a locally maximum pressure signal corresponding to aclosest first electrode, and on a next largest pressure signal valuecorresponding to a bracketing first electrode adjacent to the closestfirst electrode.
 5. A device according to claim 4, wherein each userinteraction location is estimated based on pressure signal valuescorresponding to the closest first electrode, the bracketing firstelectrode, and one or more additional first electrodes adjacent to theclosest first electrode and the bracketing first electrode.
 6. A deviceaccording to claim 1, wherein each user interaction location isestimated based on linear interpolation of the pressure signals and thelocations of the corresponding first electrodes.
 7. A device accordingto claim 1, wherein each user interaction location is estimated based onquadratic interpolation of the pressure signals and the locations of thecorresponding first electrodes.
 8. A device according to claim 1,wherein each user interaction location is estimated based on cubicinterpolation of the pressure signals and the locations of thecorresponding first electrodes.
 9. A device according to claim 1,wherein each user interaction location is estimated based oninterpolation of the pressure signals and the locations of thecorresponding first electrodes using a set of basis functions.
 10. Adevice according to claim 1, wherein the device is further configured toestimate a user interaction pressure corresponding to each userinteraction location.
 11. A device according to claim 1, wherein thedevice is configured to estimate user interaction locationscorresponding to two or more concurrent user interactions.
 12. A deviceaccording to claim 1, wherein each user interaction location isestimated based on interpolation of the pressure signals of thecorresponding first electrodes-, capacitance signals of thecorresponding first electrodes and the physical locations of thecorresponding first electrodes.
 13. A device according to claim 1,wherein the touch panel is a projected capacitance touch panel, andwherein the device is further configured to generate capacitance signalsindicative of capacitances of the first electrodes.
 14. A deviceaccording to claim 13, wherein the device comprises at least one signalsplitter stage configured to split signals received from the touch panelinto first and second signals, to pass the first signals to a firstfrequency dependent filter configured to reject the pressure signal andpass the capacitance signal, and to pass the second signals to a secondfrequency dependent filter configured to reject the capacitance signaland pass the pressure signal.
 15. A device according to claim 13,wherein the device further comprises: a projected capacitance touchpanel comprising a layer of piezoelectric material disposed between aplurality of first electrodes and at least one second electrode; and, aplurality of terminals, each terminal connected to a corresponding firstelectrode.
 16. A device according to claim 1, wherein the devicecomprises at least one amplification stage configured to amplify one ormore pressure signals.
 17. Apparatus comprising: a touch panelcomprising a layer of piezoelectric material disposed between aplurality of first electrodes and at least one second electrode, eachfirst electrode having a location; and a device for processing signalsfrom the touch panel, the device configured to: receive signals from thefirst electrodes; generate pressure signals indicative of pressuresapplied to the touch panel proximate to corresponding first electrodes;estimate one or more user interaction locations based on interpolationof the pressure signals and the locations of the corresponding firstelectrodes; and wherein the device further comprises a plurality ofterminals, each terminal connected to a corresponding first electrode.18. Apparatus according to claim 17, wherein the device is configured toreceive signals from each first electrode concurrently.
 19. Apparatusaccording to claim 17, wherein the device is configured to receivesignals from each first electrode sequentially.
 20. A method ofprocessing signals from a touch panel, the touch panel comprising alayer of piezoelectric material disposed between a plurality of firstelectrodes and at least one second electrode, each first electrodehaving a location, the method comprising: receiving signals from thefirst electrodes; generating, based on the received signals, pressuresignals indicative of pressures applied to the touch panel proximate tocorresponding first electrodes; and estimating, based on interpolationof the pressure signals and the locations of the corresponding firstelectrodes, one or more user interaction locations.